Thank you for your swift comments, guys. I really appreciate your help.
I might have misdiagnosed the problem. At least the temp directory referred in the error message seems to be there until I exit the program (after which it disappears, as it should). Here's the most recent error message:
Spoiler:
calibre, version 2.35.0
ERROR: Unhandled exception: <b>IOError</b>:[Errno 2] No such file or directory: u'C:\\Users\\[my name]\\AppData\\Local\\Temp\\calibre_6k03zy\\9vqocx_ebo ok_iter\\ops\\xhtml\\ch10.html'
calibre 2.35 isfrozen: True is64bit: False
Windows-8-6.2.9200 Windows ('32bit', 'WindowsPE')
32bit process running on 64bit windows
('Windows', '8', '6.2.9200')
Python 2.7.9
Windows: ('8', '6.2.9200', '', 'Multiprocessor Free')
Successfully initialized third party plugins: DeDRM
Traceback (most recent call last):
File "site-packages\calibre\gui2\viewer\documentview.py", line 873, in link_clicked
File "site-packages\calibre\gui2\viewer\main.py", line 573, in link_clicked
File "site-packages\calibre\gui2\viewer\main.py", line 669, in load_path
File "site-packages\calibre\gui2\viewer\documentview.py", line 922, in load_path
File "site-packages\calibre\ebooks\oeb\display\webview.py", line 44, in load_html
IOError: [Errno 2] No such file or directory: u'C:\\Users\\[myname]\\AppData\\Local\\Temp\\calibre_6k03zy\\9vqocx_ebo ok_iter\\ops\\xhtml\\ch10.html'