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If you’re still having this issue, you need to remove as many variables as possible. Since you are using a custom theme and a number of 3rd-party plugins, this is where you should focus your efforts.

Before starting this process, make a backup of your MySQL DB just in case. Also, it is advisable that you back up all your custom themes and 3rd-party plugin files just in case you make some major mistake.

Now, switch to the standard themes that come with BuddyPress. Try creating a group again. If the problem appears to be resolved, switch back to your custom themes and try creating a group again. If the problem returns, contact the theme designer.

Next, assuming the problem still exists with the standard BuddyPress themes, you should deactivate your 3rd-party plugins one at a time. Deactivate just one, try creating a group again. If the problem still exists, then deactivate another 3rd-party plugin. Keep doing this until either the problem goes away, or all 3rd-party plugins are deactivated. You can also go about this the other way: deactivate all plugins except BP and then reactivate one at a time, checking to see if the issue occurs again with each new reactivation.

If you find that the problem goes away after a particular 3rd-party plugin is deactivated, then you may have found the culprit. Contact the developer of that plugin and ask for advice.

Please report the results back in this thread.