Unexpected file format

[Mortar]

I get this error all the time when I want to open my RMXP project:

'Unexpected file format.'

It was working fine just yesterday and now it won't even load! Does anyone know how to fix it?

[afterlife]

im not to sure but there is probably a file that has a different format than what rpg maker uses... but im not to sure
if that is the case then you could try changin the file formats but again im not to sure on how to do that...

[Mortar]

Well, I found a solution, I just copied all of the 'broken' projects' files and pasted them in a fresh project. Lock please.

[firerain]

I tried your solution, it doesn't work for me. If anyone knows how to fix it, please share.

I get "Unexpected File Format" when I try to open my project.