Receipt in AR got the customer field not editable

Hi experts

   There's a receipt in AR which does not have the customer name / # assigned but the fields are not editable to enter.

   The receipt was applied to 3 invoices with 2 differente customer #'s.

   Do you know if that might caused the problem ?  Now the receipt can not be updated to do any action.

   Is there a concurrent or a process that can release the receipt so customer fields can be modified?

Please advise

Thanks in advance,

Claudia