Internal program error 1646.k.bm.mp

[SpecialistSupps]

Hi,

I built a website in Web Designer Pro 7 a few months back, which published fine. Yesterday, I went back into the file (now using Designer Pro X) to add new content and on trying to upload it, the internal error message above appeared (see the screenshot attached). It won't allow me to save it either. It simply says 'unable to save' and then closes down.

I have tried using back-up versions, re-saving the file as a new name etc and the same error message keeps coming up.

Does anyone know what could be causing this error?

Thanks!