Does anyone have any suggestions of what might cause this? Is the workaround in this thread from 2008 still valid? Can't delete a custom property column.
I wouldn't try removing the column from the database, just in case there's other bits hanging about post-deletion that you can never clear up (from the database views and so on). Couple of things:
If all else fails, run the Configuration Manager, checking the website option, which will repair the website/permissions.
Hope this helps!
DISCLAIMER: Make sure you have good backups of all servers and databases before running the Configuration Manager. If you're risk averse, also consider these checks before starting/stopping the services.