I'm using the Canon Photo Professional program that comes with Canon DSLR's.
Last night I came across a problem.
Anytime I make changes to a photo, whether it be cropping, sharpness, etc... and I try to "convert and save" it, it comes up with the error "Cannot write to file"
I've never had this problem.

Does anyone know what is causing this problem, and/or how to fix it?

Yeah, sorry for trolling but kick off that shity program and install fast Stone image viewer, LR 2 or 3 or PS and you good to go.
Or just make an update of your program...

I would love to be able to use LR2/3 or PS, but I don't have them nor do I have the money for them atm.

but thats why you got internet

I'm not knowledgable enough with torrents to be able to find a good download for them though