I am using the 3.2.0.2 Basecamp Beta.
I forgot to reset my Garmin 450 between rides on June 14 and 16. I was able to upload the combined track to Garmin Connect but did not like the combination. I split the gpx in Basecamp by deleting the June 14 points from one copy of the track and the June 16 points from another copy. After that I could not load either track into Garmin Connect. I just get the message:
"An error occurred with your upload. Please try again."
I tried both Firefox and IE9 with the same result. I am including the original gpx and my 2 modified gpx's for you to look at. These have not been exported by Basecamp. They are right off of my 450.