error/group/erroraddremoveuser

This error is produced by the code in /group/members.php which calls code in /group/lib.php which in turn calls code in /lib/dmllib.php.

The various functions involved result in a line of SQL which is sent to the database engine.

You can trap this SQL in /lib/dmllib.php with a line like

print("SQL to be run is $insertSQL");

if you insert the line at line 1555 in /lib/dmllib.php.

The text "SQL to be run is INSERT INTO ....." will then appear at the top of the page that is causing the problem. You may then be able to debug the problem.