I am having this issue, but the file size limit isn't why. I have a bug report I'd like to post, but for Steve to find it, he'll need my DB. I have tried both zip and 7z file types. Zip results in a file size of 4601KB, while 7z results in 2954KB. These are *well* below the 500MB files size limit listed on the attachment restrictions below.
"Restrictions: 4 per post, maximum total size 1048576KB, maximum individual size 524288KB"
Any thoughts?