BartMan01,
I think others are having similar problems and the JRiver team is trying to sort it out. Most of the time my iPod syncs are also freezing up MC.
I've tested different combinations trying to pick up a pattern. I just had 2 successful syncs of ~15,000 tracks each, so maybe a pattern is emerging.
I have a fall back as I can sync with iTunes. It sounds like you are stuck so I'll share what I've had the most success with, even though it is preliminary information, in case it helps you.
EDIT: 0) Make sure you are current on your iPod firmware
1) Reboot your PC. I've gotten inconsistent results after trying multiple syncs where I had to manually terminate MC. I think a reboot eliminates this variable.
2) Turn on logging. At least if it fails you can share a log with the JRiver team. I think you know how to do this. It is on the help menu.
3) Initialize the iPod before starting. The hang/freeze leaves the iPod database in a corrupt state.
4) Open task manager or something that allows you to monitor CPU usage.
5) Start the sync
6) Minimize MC. Task manager is now your 'eyes' to monitor if the sync is progressing. My syncs take ~10-20% of the CPU.
7) If CPU usage drops - the sync is done. It may have froze, or it may have competed. If you can maximize MC, it probably completed
The theory behind the minimize is that the freeze/hang is not related to the data upload, but some other process that occurs when MC is running the sync operation. This process may be specific to a certain view(s), or something like that. In other words, this is just a guess.
If you try this, let us know if it worked or failed.
Randy