Some of KWizCom products add event handler to SharePoint lists. Unfortunately SharePoint do not provide any tool which allows to remove broken Event Handlers.
This error occurs because the list contains event handlers for SharePoint List Forms Extensions Feature that should be removed.
We suggest using the following tool.
How utility works?
The utility removes the assembly name that you provide in theparameter. If it is empty it will remove all the event handlers.
One of the parameters is string for assembly name. You can putfull name or partial name; it should only remove event in which you specified.
"Enter Event Handler Assembly Name (You can enter full orpartial name. For example: