Upload Problems with GIMP

I downloaded GIMP and everything else I need in order to use it. I made a test sig named Sig1.xcf (GIMP said .xcf helps with layers or something so I did what it told me to do) then I changed it from .xcf to .jpg so I could upload it in imageshack, I keep getting this error message and I'm not sure why: File integrity check failed, upload terminated.

Anyone know how I can fix this?

If it says that try going to Image>flatten image. That's what I have to do if I want to save something in jpg. After that it should ask you for like jpg quality, and it's fine where it is on the slider bar. Just be sure to put file type> all files. Then put .jpg on the end of it.

usually easier in file>save a copy as

Alright, I'll give it a try peeps. :D