Perhaps you have duplicate GUID or System Names. Take a look under Queries and look for the stock query for "Duplicate Systems Names" or "Systems with High Sequence Errors".
If that is the case then under the "Server Tasks" there is a stock sever task "Duplicate Agent GUID" which will remove (delete from ePO)duplicate agent GUID. Caution: make sure that is what you want to do.
Hey, thank you for your reply!
but I still don't understand what is the problem... Can you please try to explain it to me?