Hi! First off I'd like to say hats off to Kovid Goyal for making Calibre, which I'm an avid user of. For the longest time I didn't update (because for me Calibre was flawless, why update?) but then I saw 0.9.18 and realized I probably should upgrade. So I went about and downloaded the installer for the newest version of calibre.
Already I encounter my first problem. Just after installation completes, in a dialog box a message pops up: "There is a problem with the Windows Installer Package. A DLL required for this install to complete could not be run. Contact your support personel or package vendor"

I'm not sure what to make of it.
I'm running Windows 8 Pro 64-bit and had downloaded the 32-bit installer. It obviously made sense to me to uninstall the 32-bit calibre and install the 64-bit calibre, which I did with the exact same error. Next I tried uninstalling, rebooting my computer, and then reinstalling the 32 and 64-bit ones. At that stage I realized it 32-bit and 64-bit didn't affect the problem.
Later I discovered that Calibre still runs, but the amount of errors it runs on is driving me nuts.
While trying to view a book, this is the error:
Spoiler:
calibre, version 0.9.18
ERROR: Could not open ebook: [Error 5] Access is denied: u'C:\\Users\\Tashfin\\AppData\\Local\\Temp\\calibr e_0.9.18_tmp_8so6du\\xnwmcj_ebook_iter'
Traceback (most recent call last):
File "site-packages\calibre\gui2\viewer\main.py", line 40, in run
File "threading.py", line 504, in run
File "site-packages\calibre\ebooks\oeb\iterator\book.py", line 99, in __enter__
File "site-packages\calibre\customize\conversion.py", line 234, in __call__
File "site-packages\calibre\__init__.py", line 437, in __enter__
WindowsError: [Error 5] Access is denied: u'C:\\Users\\Tashfin\\AppData\\Local\\Temp\\calibr e_0.9.18_tmp_8so6du\\xnwmcj_ebook_iter'

I'm not sure what to make of it.
So I quit trying to read it. Next I tried converting a book for a friend who wanted to read it, from epub to epub and from epub to mobi, and the same error occurs:
Spoiler:
calibre, version 0.9.18 (win32, isfrozen: True)
Conversion Error: Failed: Convert book 1 of 1 (All He Ever Desired)
Convert book 1 of 1 (All He Ever Desired)
Qt: Untested Windows version 6.2 detected!
Resolved conversion options
calibre version: 0.9.18
{'asciiize': False,
'author_sort': None,
'authors': None,
'base_font_size': 0.0,
'book_producer': None,
'change_justification': u'original',
'chapter': u"//*[((name()='h1' or name()='h2') and re:test(., '\\s*((chapter|book|section|part)\\s+)|((prolog|pr ologue|epilogue)(\\s+|$))', 'i')) or @class = 'chapter']",
'chapter_mark': u'pagebreak',
'comments': None,
'cover': u'C:\\Users\\Tashfin\\AppData\\Local\\Temp\\calibr e_0.9.18_tmp_8xrayp\\oluqkn.jpeg',
'debug_pipeline': None,
'dehyphenate': True,
'delete_blank_paragraphs': True,
'disable_font_rescaling': False,
'dont_split_on_page_breaks': False,
'duplicate_links_in_toc': False,
'embed_font_family': None,
'enable_heuristics': False,
'epub_flatten': False,
'extra_css': None,
'extract_to': None,
'filter_css': u'',
'fix_indents': True,
'flow_size': 260,
'font_size_mapping': None,
'format_scene_breaks': True,
'html_unwrap_factor': 0.4,
'input_encoding': None,
'input_profile': <calibre.customize.profiles.InputProfile object at 0x03EC50D0>,
'insert_blank_line': False,
'insert_blank_line_size': 0.5,
'insert_metadata': False,
'isbn': None,
'italicize_common_cases': True,
'keep_ligatures': False,
'language': None,
'level1_toc': None,
'level2_toc': None,
'level3_toc': None,
'line_height': 0.0,
'linearize_tables': False,
'margin_bottom': 5.0,
'margin_left': 5.0,
'margin_right': 5.0,
'margin_top': 5.0,
'markup_chapter_headings': True,
'max_toc_links': 50,
'minimum_line_height': 120.0,
'no_chapters_in_toc': False,
'no_default_epub_cover': False,
'no_inline_navbars': False,
'no_svg_cover': False,
'output_profile': <calibre.customize.profiles.iPadOutput object at 0x03EC5370>,
'page_breaks_before': u'/',
'prefer_metadata_cover': False,
'preserve_cover_aspect_ratio': False,
'pretty_print': True,
'pubdate': None,
'publisher': None,
'rating': None,
'read_metadata_from_opf': u'C:\\Users\\Tashfin\\AppData\\Local\\Temp\\calibr e_0.9.18_tmp_8xrayp\\_bh6ba.opf',
'remove_fake_margins': True,
'remove_first_image': False,
'remove_paragraph_spacing': False,
'remove_paragraph_spacing_indent_size': 1.5,
'renumber_headings': True,
'replace_scene_breaks': u'',
'search_replace': '[]',
'series': None,
'series_index': None,
'smarten_punctuation': False,
'sr1_replace': None,
'sr1_search': None,
'sr2_replace': None,
'sr2_search': None,
'sr3_replace': None,
'sr3_search': None,
'start_reading_at': None,
'subset_embedded_fonts': False,
'tags': None,
'timestamp': None,
'title': None,
'title_sort': None,
'toc_filter': None,
'toc_threshold': 6,
'unsmarten_punctuation': False,
'unwrap_lines': True,
'use_auto_toc': False,
'verbose': 2}
InputFormatPlugin: EPUB Input running
on C:\Users\Tashfin\AppData\Local\Temp\calibre_0.9.18 _tmp_8xrayp\bjiiwr.epub
Python function terminated unexpectedly
[Error 5] Access is denied: u'C:\\Users\\Tashfin\\AppData\\Local\\Temp\\calibr e_0.9.18_tmp_8xrayp\\iux_nh_plumber' (Error Code: 1)
Traceback (most recent call last):
File "site.py", line 132, in main
File "site.py", line 109, in run_entry_point
File "site-packages\calibre\utils\ipc\worker.py", line 189, in main
File "site-packages\calibre\gui2\convert\gui_conversion.py", line 31, in gui_convert_override
File "site-packages\calibre\gui2\convert\gui_conversion.py", line 25, in gui_convert
File "site-packages\calibre\ebooks\conversion\plumber.py", line 1009, in run
File "site-packages\calibre\customize\conversion.py", line 234, in __call__
File "site-packages\calibre\__init__.py", line 437, in __enter__
WindowsError: [Error 5] Access is denied: u'C:\\Users\\Tashfin\\AppData\\Local\\Temp\\calibr e_0.9.18_tmp_8xrayp\\iux_nh_plumber'

I'm not sure what to make of it. This error occurs in any instance of converting, for ANY book. All DRM free.
Afterwards, I tried retrieving a metadata and book covers for the same book. This error occured with the other books too, once again, DRM free. The error is that metadata would fetch fine (even if it did take a bit longer than usual), but the cover art wouldn't come up at all. This is what I get:


I'm not sure what to make of it. And at this point, I'm angry and determined to solve this problem.
The rest of the features seem to be working (i.e. adding books, retrieving metadata, saving to disk, it's only the few up there [the ones that I happen to use the most] that are causing problems).
So these are the steps I took to try to solve it:
Spoiler:
1. I cleaned up my local drive using CCleaner (by Piriform), no luck.
2. I installed Calibre portable. The windows installation error left, but the convert and cover art error was persistent which baffled me.
3. I downgrade to v0.9.17, same error.
4. I tried installing calibre at a different place but it wouldn't allow me, I got this error: "Install Calibre on the local hard drive", or something like that. The thing is, I was installing it on my local hard drive (C

, but the error was persistent. So was I.
5. I opened calibre and then went to the place where calibre stored it's temporary files. There were different folders, one that popped up each time it executed an action. Like there was one when I tried converting. One when I tried retrieving book data. One when I tried viewing a book. Stuff like that. I proceded to change all the folder attributes. I noticed that they were Read-Only (but to specific files and folders), so I made them all fully read-only. One time, it had worked and then it stopped working the next time I launched calibre and tried converting again.
6. I uninstalled callibre, went to the app data folder, went to roaming and deleted all of calibre's stuff. Then I went to local, temp, and then deleted all of calibre's stuff there. Then I went and redownloaded calibre (in fact, I've redownloaded calibre 4 or 5 times), and the same issues are there.
7. It's not a virus, I just did a complete virus scan using avast, and windows defender is off.
8. In windows firewall, calibre is not blocked, and I have given it further permissions of everything.
9. I cleaned my registry for any errors, no good.
10. I've read other threads, and they haven't been of much help.
IDK what I should do. Is it Calibre? Windows? Or some third-party issue?
I'm great with computers. Throw any computer lingo you got at me, I'll understand. Any help/insight on the situation is welcome

If you've read and considered this thread up to now then