Saving Dreamweaver files
When I'm building emails in Dreamweaver CC (Mac) occasionally (getting more often) I get the message as below.

It usually happens when I've already built and saved it, put it to the Server and previewed it in a browser. Then if there's a small mistake I go back to Dreeamweaver to correct it and then I can't save it. Other Dreamweaver files that are open at the same time will save fine but not the one I'm currently working on?
Very frustrating and always happens when I've got a tight deadline!
Thansk in advance
