Calibre Won't reopen after setting change (Ubuntu 16.04 LTS)

[alkh3myst]

I have Calibre installed to manage content on my Kindle Paperwhite. Yesterday, I opened Calibre, and its window was so large, I couldn't close it (clicking the "x"). The Calibre menu has no "file" tab, so I couldn't close it that way. I decide to add its icon to the system tray, and select this from settings. When I reopen Calibre, I get the message: "ERROR: Startup Error". How do I edit this error? I don't know which entry to change in the configuration file. ALSO: I have repeatedly purged Calibre and its dependent package, "calibre-bin" from my system, then reinstalled, but I can't get a default configuration file. Further, I've 1. Logged out and back in before reinstalling, 2. Restarted before reinstalling, and I just 3. Reinstalled after installing a kernel update. What gives? Why won't repeated reinstlls generate a fresh configuration file? I've started searching for the hidden configuration files that may be stopping me from getting a clean reinstall, but there are dozens that I will have to manually delete. Is there an easier way to get Calibre back up and running properly? Is my problem something else entirely? Here (below) is the error readout I got from "show details":

calibre, version 2.55.0
Traceback (most recent call last):
File "/usr/lib/calibre/calibre/gui2/main.py", line 276, in initialize_db_stage2
self.start_gui(db)
File "/usr/lib/calibre/calibre/gui2/main.py", line 216, in start_gui
main.initialize(self.library_path, db, self.listener, self.actions)
File "/usr/lib/calibre/calibre/gui2/ui.py", line 261, in initialize
self.system_tray_icon = factory(app_id='com.calibre-ebook.gui').create_system_tray_icon(parent=self, title='calibre')
File "/usr/lib/calibre/calibre/gui2/dbus_export/widgets.py", line 232, in create_system_tray_icon
ans = StatusNotifierItem(parent=parent, title=title, app_id=self.app_id, category=category)
File "/usr/lib/calibre/calibre/gui2/dbus_export/tray.py", line 44, in __init__
self.dbus_api = StatusNotifierItemAPI(self, **kw)
File "/usr/lib/calibre/calibre/gui2/dbus_export/tray.py", line 114, in __init__
self.dbus_name = BusName(self.name, bus=bus, do_not_queue=True)
File "/usr/lib/calibre/calibre/utils/dbus_service.py", line 238, in __new__
raise NameExistsException(name)
NameExistsException: Bus name already exists: org.kde.StatusNotifierItem-18241-1

I appreciate whatever help someone can offer, thanks.

[alkh3myst]

Update: Output of calibre-debug-g

calibre 2.55 embedded-python: False is64bit: True
Linux-4.4.0-81-generic-x86_64-with-Ubuntu-16.04-xenial Linux ('64bit', 'ELF')
('Linux', '4.4.0-81-generic', '#104-Ubuntu SMP Wed Jun 14 08:17:06 UTC 2017')
Python 2.7.12
Linux: ('Ubuntu', '16.04', 'xenial')

[kovidgoyal]

You want to delete calibre preferences, they are in ~/.config/calibre

[alkh3myst]

Sorry, I don't see that file (directory?). Is there somewhere else it could be?

alkh3myst@R:~$ cd ~/.config/calibre
alkh3myst@R:~/.config/calibre$ ls
conversion global.py history.plist plugins
dynamic.pickle gui.json iterator.pickle tweaks.py
fonts gui.py metadata_sources viewer.json
alkh3myst@R:~/.config/calibre$ ls -a
. dynamic.pickle gui.json iterator.pickle tweaks.py
.. fonts gui.py metadata_sources viewer.json
conversion global.py history.plist plugins
alkh3myst@R:~/.config/calibre$

[kovidgoyal]

rm -rf ~/.config/calibre

[alkh3myst]

I should have realized you meant delete the entire directory! I was very tired that night. I feel like an idiot now, LOL! That worked fine, thanks so much.