Hi vvnlens, sorry you’ve run into this issue.
A couple things to try.
1. Update to 2.9.1 and see if that fixes things. I suspect it may not though.
2. Check that your database is set up correctly. This kind of error sounds like what happens when there is something wrong with the database or the PMPro tables in the database. Make sure the wp_pmpro_membership_levels table is there. (It may have a different prefix than wp_) Make sure the table is not corrupted or in need of “repair”. Make sure you haven’t run out of disk space for the DB.
There was a rare bug with some hosts that for some reason kept trying to insert the first level into that table with an ID of 0 which would break on some set ups. So (working with your host if you don’t know how to do this) increasing the “autoincrement” value to 1 on the wp_pmpro_memberships_levels table would sometimes fix this.
You can look for errors in your MySQL log or PHP error log around the time you get the “error adding membership level” error, and if you see something there, that might give a clue as to what is going on.
I hope you can figure this out soon.
