Bem, parece que eu sou capaz de reproduzir o problema no meu final, bem depois de baixar o acrobat do Adobe mais recente. Portanto, não é "apenas" o usuário. Agora que tenho a mensagem de erro, consegui encontrar informações para o problema. Parece ser um problema com o novo release 11.0.10 da Adobe e o modo protegido.
Informações AQUI
My users started to experience this issue for files on network shares as well once Adobe Reader was updated to 11.0.10.
It has to do with Protected Mode being turned on. I don't know if it was off by default & now it is on with the update but turning it off changes Adobe Reader's behavior back to what the users expect - a prompt warning you if you want to overwrite the existing file & then selecting Yes to overwrite.
To disable Protected Mode:
Start Adobe Reader
Edit - Preferences - Security (Enhanced)
Uncheck Enable Protected Mode at Startup
Close Preferences & Close Reader
Now open a file from a network share & you Adobe saves as it used to.