One of our customers sent me two Excel XLA add-ins. When I tried to open that file in the VBA Editor — the "Project is locked" message appeared. Add-in has been already unlocked by our VBA password recovery tool. According to Microsoft article this message may appear in two cases: when the macro is protected by password or when it is digitally signed. I analysed the macro password record and found that the password is empty. MS Excel also showed me that macro have no any digital signatures. Then I looked into protection record with more attention and for example found that:
"[Host Extender Info]" string is replaced to "[Host Extender 1nfo]".
There were some additional similar changes and finally I found that the macro has damaged digital signature record. It’s ignored when macro is running but when we try to open the macro to view — Excel shows the error.
Microsoft has very weak VBA macro protection. That’s why developers are searching for non-standard protection methods. It’s not simple to reconstruct a damaged macro and it may require a lot of time.
If your macro cannot be opened by our password recovery programs — the most probable reason is custom protection that damages some technical records. I cannot say that it’s a good protection. New versions of MS Office may not work correctly with damaged files.