In case it's an event of the type "Event / Approve", the names of the used browse actions are SelectSingleUser for the "User who approves content" and SelectMultipleUsers for "Excluded user groups".
I am using "Event / Approve" event type.
When I try to add user from my custom user class to "User who approves content" checkbox of user is disabled!?
Try restarting your browser. eZ will often use browser session variables to hold data which can only be removed by ending the session. If i remember right this is one of those occastions.
