Make sure you are running Flash 9, also make sure the file extension is correct. 

Yes on both counts. Flash 9 and .jpg file.  I had Flash 10 but downgraded to 9 to try and fix this problem but still no luck. I uploaded a skin last week and nothing had changed inbetween times. So I'm baffled. I even tried renaming the screenshot, thinking maybe it was the characters in the name. But no go. I still get the same error message.

What url are you uploading to, Imzadi?

The one you get when you click on "submit to gallery".  Let me see.... it's https://www.wincustomize.com/upload2.aspx

I tried the old upload link that somebody posted in another thread but it didn't work either.

Yep...you're using the right url. I wonder if you could simply email the file to one of the Mods and he/she could help you...?

I wouldn't mind doing that. Anybody want to help out?  I would still need to know what the problem is so I could upload in the future.

Mods can't upload files for you. But...

...how did you get rid of 10? From what I hear you have to zap it, just uninstalling doesn't work. This may be your problem.

Fuzzy is correct,according to Adobe,you must use their uninstaller to remove Flash 10 )   LINK

I did use their uninstaller to uninstall it. Then downloaded the Flash 9 pack, and picked one of those to install. It's showing as Flash 9 when I check it.

Okay. Let me be specific as to what I did.

I went to upload the skin and it kept failing. I tried it with two different screenshots and different file names and the same thing happened. So I came here on the forums and read that sometimes Flash 10 can cause problems with uploading. So I went and got the uninstaller, uninstalled Flash 10, restarted my computer, installed Flash 9, restarted the computer and am still having problems, even though it's showing Flash 9 is on my system. It still says the same thing. That the screenshot is invalid and that I have to have a screenshot to upload a skin. I can try another screenshot but I would imagine it  would be the same problem.

WAIT! The screen shot has to be at least 1024x768 resolution. Is your screen shot that size?

Yep. 1152 x 1665

Actually thought I had it there for a second. Is it .jpeg format?

edit...just saw it was.

email Jafo. ask if you can send the file for examination...

What is the file size of the screenshot...in MB?  Sometimes, if it's too high, WC won't take it.

2.94 MB.

I just PM'ed Jafo so we'll see.