I didn't see a specific size limit anywhere but I am guessing somewhere around 10mb. Is this the case?
Updated
Posted under General
Biggest flash is over 60MB, it might be that your connection is too slow to send requests larger than 10MB fast enough for the server to accept them. I don't think there's much you can do here other than keep below 10MB, unfortunately.
Log said:
There are but they're high enough the average user shouldn't notice them.
Oh right, I remember when that 100MB .png was posted there was a discussion to lower them it so png_overkill can be avoided. Had forgotten about that.
Well post #420282 is 69 megs, but that was posted by a Contributor and a year ago. Though post #494650 was uploaded by a Member and it's 25 megs, but again posted a year ago, so make of it what you will.