It's either a failure with the Twitter utility recognizing the file type as what the extension declares, or the file itself is in an mp4 wrapper but the codec itself is not actual mp4.

Try renaming the file to mpg, or mpeg, or mpeg4 (before you do though, make a few copies)

good suggestion but mpeg and mpeg4 give an error message of ... 'this kind of file isn't supported yet.Try uploading a gif, video, or picture instead'.

i tried uploading the exact same video and using the exact same video if i trim the first 2 seconds off using the 'trimmer' built into twitter, then the video uploads no problem. however this video is 10 seconds long, i don't want to cut the first 2 seconds off!

i've tried again full length and just got a 'dead bird' icon. i've never seen this before, but the meaning is clear.

as i said facebook processed the same video no problem, it is no wonder twitter is going down the drain!

Well, you could try just renaming it (keeping the same file extension.) Twitter likes to cache by filenames. Tricking it into thinking this is a new file might work.

ok, i'll try that next time, that's a good suggestion.
in the end i trimmed the first second off the video, using the twitter trimmer tool and it accepted it!
thank you for your help.