I am a Vimeo Plus user as well. 5GB is your weekly max that you can upload. Individual files, however, have a smaller limit. I could be mistaken, but I believe a single file cannot be longer than 1GB. Remember that Vimeo will re-encode your file to around 1.5Mbps and 720p to show it from the Vimeo site. So, if you are encoding using some ultra high quality settings, you don't need to. I encode to 1280x720 at 2 to 4 Mbps with 24 keyframes and it usually produces files that are around 400 MBytes to 600 MBytes for about 45 minutes of high def video. Also, you might want to use their webpage uploader instead of the desktop uploader. Folks have experienced problems with their new desktop uploader. Best wishes.
Yeah I'd do a manual test. Share out the file as Export Movie, pick the H.264 setting from the Export drop down. Then upload that manually to Vimeo. It sounds more like an account limit issue than an FCP X issue. Unfortunately it seems X has no way to get feedback from Vimeo before trying to send a video- limit of the way that site works.