I can't upload my swf files to online video converters that support swf?

I'm trying to convert my fla or swf file to avi, however it seems none of the online converters can take it. I keep getting the error message saying that my swf file is not supported by the converters, when they clearly state that swf is a supported format. It's not just one converter though, I've tried about 4 sites, and I'm beginning to think that there's something wrong with my flash file instead?