Weird Error Message in X8

I've suddenly been receiving this strange error message when opening a previously saved file. It just started happening, it reads;

"This file originated from another program. You can open and edit it but doing so may discard some of the original information that was in this file"  

All my drawings originate from X8, and I haven't saved the file in any other place but the original folder.  Would it be because I added some macros? Anyone have an idea what is going on? The files do not seem to be altered in any way but I would like to know the reason for this. 

Thanks, Iain