Problem Uploading to Downloads

I recently completed a tower model as part of a request and I would like to put it up for download in the models section of the Downloads forum. However, once I click "submit file," fill out the appropriate text boxes, and click the submit button I get an error message stating that there was an extension error. I've attached a screenshot of what the form looked like before I tried to submit it. If there is an error with what I have written or if I'm going about uploading files the wrong way, let me know so that I can finally upload my file to download.

Your screenshot extension ends in ".JPG", make it ".jpg" and it will work.

That was the problem. I submitted it again and there was no error message. Thank you for your quick reply and your help.

Hey, I am having a similar problem. When i click submit file or submit download in the download section, it says invalid link.. pls HELP

i cant post when i click on submit file it comes up with error
i have posted files before but now i cant.....

It came up with extension error someone help me please?