Here's a fairly significant new problem. I've updated to the latest rev of 7.9 and removed the tweak database plugin. I stopped the server, deleted everything in the cache, then restarted. The server fails to scan the library and scanner.log shows the following:

Code:
[14-05-10 02:44:33.7133] main::main (202) Starting Logitech Media Server scanner (v7.9.0, TRUNK, UNKNOWN) perl 5.014001
[14-05-10 02:44:34.4477] Slim::Schema::forceCommit (2109) Warning: Trying to commit transactions before DB is initialized!
[14-05-10 02:44:35.1040] Slim::Utils::DbCache::_init_db (275) Warning: DBD::SQLite::db do failed: SQL logic error or missing database
cannot VACUUM from within a transaction at C:/Program Files (x86)/Logitech Media Server 7.9/server/Slim/Utils/DbCache.pm line 243.
Delete the file C:\ProgramData\Squeeze\70\cache\artwork.db and start from scratch.
[14-05-10 02:45:08.0571] main::main (298) Warning: Issuing rollback() due to DESTROY without explicit disconnect() of DBD::SQLite::db handle dbname=C:\ProgramData\Squeeze\70\cache\artwork.db at C:/Program Files (x86)/Logitech Media Server 7.9/server/scanner.pl line 298.
[14-05-10 02:45:08.0574] main::main (298) Warning: Issuing rollback() due to DESTROY without explicit disconnect() of DBD::SQLite::db handle dbname=C:\ProgramData\Squeeze\70\cache\artwork.db at C:/Program Files (x86)/Logitech Media Server 7.9/server/scanner.pl line 298.
[14-05-10 02:45:08.0580] main::main (301) Error: Failed when calling Slim::Schema->wipeAllData: [Unable to read/create C:\ProgramData\Squeeze\70\cache\artwork.db]
[14-05-10 02:45:08.0583] main::main (302) Error: This is a fatal error. Exiting
I can manually run a full wipe and rescan after this and the library is scanned successfully, with scanner.log showing no errors.