Byte Stream Type on Audition

Hi there, was working on a Multi-track mix last night. It's a .sesx file. I saved and closed as normal and have gone to open it this morning to find it unable to open due to the following error:

"Error Media foundation reported an error when opening the file. 

The byte stream type of the given URL is unsupported" 

I'm really confused as to what this is? I've never had this issue with Audition before, and put a heck of a lot of hours into this so really hoping I can get back into it. Any help much appreciated!