We'll work with you to make sure your file gets posted is one piece, as this is certainly a "must have" contribution. I sent you an e-mail. Sorry you had a problem.
There are a number of reasons we decided to limit the attachments to only gpx files. Firstly, they are non-proprietary and open to all platforms. Secondly, mps files have been superseded by the newer format (Garmin has a habit of changing their file format frequently). Lastly, Garmin files are not easily authenticated allowing viruses to potentially be transmitted under cover. I too would like to share Garmin files, but alas, the GPX file is so simple to translate that it makes sense.
I hope this works for you since we would love to see some of your stuff posted now and in the future.