Recently I encountered this strange error message in WordPress when trying to write a new post. Maybe I haven’t done any major changes, only removed a security plugin recently while the whole system is continuously updated.
Disabling all plugins and reverting to the standard twentyfifteen theme did not help. Inspection of post.php also did not show anything unusual (the indicated line number was probably wrong due to several includes). Googling the error message also did not help as these lead only to site specific problems.
A manual SQL insert attempt via the PHPADMIN interface did not work giving me a first direction. When looking at the mysql grant rights, I found that the INSERT command was disabled (all other commands were possible). As I can not configure the database on this hosted system, I hat to call the service provider. He told me that I reached a database quota during the last night that he cannot lift.
So I had to dump the whole database and restore it as a new database. My database limit of 10 MB seemed to goes back to July 2006 when I installed WordPress 2.2.1 …