Hi Everyone. How to resolve this error : SETFIELDVALUE [Warning: Value cannot be set in BEFORELOAD on already existing (not a new) record.] Case: Trying to uncheck a field based on another field in the same record. This is for earlier created transactions and future transactions as well.

It's exactly as stated you cannot update an existing field in the beforeLoad. You should move logic that sets fields to the beforeSubmit and set the field value on the newRecord object. The only time you can set a value in beforeLoad is if you're _adding the field first a_nd that field would start with the internalid id of "custpage"