Project does not open (#2736)

Hi, I'm starting a new project from existing C# source code.

I'm able to import my solution and everything seems to work, I just need to adjust some diagrams, add some comment, and add a couple of function diagrams.

I save the project to do other stuff later.

To my surprise, I'm not able to open again that project and I'm getting a message "File .... does not contain software ideas modeler in any supported format". I've also tried to make a new project starting from the same solution file saving it right away with no changes: same result!

Please help, I need to have these diagrams for a very important project ASAP!

TY in advance