Thread:Project:Support desk/"Error: 14 unable to open database file"

Continuation from this thread

Recently, I've been having problems with certain functions on my domain http://grisaiawiki.net When I try to protect, undelete, or move a page, I get errors preventing me from doing so. After enabling the appropriate settings, I now get the following message when trying to do any of these: (this example from trying to protect the Main Page from non-administrators)

A database query error has occurred. This may indicate a bug in the software.

Query:
 * UPDATE page SET page_restrictions = '' WHERE page_id = '146'
 * Function: WikiPage::doUpdateRestrictions
 * Error: 14 unable to open database file

I still can't figure out why I'm having this issue, or even what's causing it. I've never made any changes to files like DefaultSettings.php or WikiPage.php, nor have I touched anything in /includes/db/. None of my extensions or changes to LocalSettings.php seem to have caused it either, as removing/undoing those changes doesn't help. I'm at a complete loss by this point.