I had a problem last night where I couldn't upload from my garmin using chrome on my desktop pc, I had the same problem
AliC just wrote about, which prompted me to write this... not just me!
I managed to get it to work on my laptop, using chrome, after installing the garmin software fresh. I guess it could be a matter of upgrading the software but given I'm not the only person perhaps there is something else going on. Has anyone else had this problem?