I was trying to upload a new version of the art tool I have freely available in the GDNet Marketplace.
Unfortunately, when I try to upload the file, it says the upload failed because the file was too big.
The file is only 5.86 MB, and it says that I can upload files that large.
The upload page says, "Maximum file size is 23.84GB." - that might be a bug in itself, unless you're planning for us to upload HD DVDs. 
Are you trying to upload directly with the form on the page, or are you using FTP?
That maximum upload size is correct, although I think the biggest individual file we have is this one, weighing in at 1.51GB.
I used the form on the page, and when that failed twice, I used the "Trouble uploading? Try switching to our basic uploader" form which failed with the same message.
Did you try logging into files.gamedev.net with your gamedev.net username and password? If you upload files via FTP you can just enter the filename into the text input box after clicking "Submit file uploaded to files.gamedev.net (enter filename of file)".
