@elofran thanks for this, appreciate much.
Although for me 'the staff' still doesn't populate on the dashboard after clicking to add staff, the operation is successful somehow (i can't explain it) but when you click to view all staff created then it triggers the database error. This is just what i have from my test.
Prior to your modifying, the manager and group creation had similar database errors, but now group and manager are fixed... only staff doesn't for me.
Using the advanced Db Cleaner,i don't seem to find the error table wcfm-store-staffs either.
Weldone sir