Error when sending mail

I have two users that everytime they go to save a Calendar Entry or Send an e-mail that they get an error that says “cannot execucute the speceified command”

I had them remove there signature file and also replace the design of there mail file. I’m looking for any other ideas on how to fix this.

Subject: Narrow it down

Try sending an email using the same mail file, but from another workstation and see if you can reproduce the issue. This will help narrow it down to the workstation or the mailfile. If it is the mailfile, try making a new copy.