Invalid User ID when changing permissions

HI,

I recently migrated my existing WP database and a new instance of WP to a new server (the resources weren’t high enough to run Registration Spam protection) from https://www.bewitching-fiction.com to https://www.bewitching-forums.com.

I have 4 active plugins on the site (each of which are brand new instances) and I have activated and deactivated them in an effort to fix this but obviously in order to do what is causing the error I need two of them active by default:

Buddypress 2.3.3
BBpress 2.5.8
WP Supercache 1.4.5
Antispam by Cleantalk 2.25.2

I am trying to update the permission levels on the forums of four of my users from Participant to Moderator. One went absolutely fine, no problem at all, then I attempted to do the last three and got 2 errors:

The first one appeared immediately after I clicked on ‘Save’ for the change from participant to moderator

“Internal Server Error – Read

The server encountered an internal error or misconfiguration and was unable to complete your request.
Reference #3.b64bf6d8.1443948567.c9c1a6c”

The second appeared when I refreshed and attempted to try again

“Invalid user ID.”

Now, apart from removing a member in the database I have made no further changes to the SQL, but this keeps on occurring. Please let me know if there are any fixes I can try – I am at my wits end here.

Thanks