I also found that 5.0.5 doesn't work, though for different reasons. In my case it thought my license to upgrade had expired (though it doesn't until near the end of this month). Unfortunately I then tried a patched 5.0.5 that left me unable to run 5.0.4 either (though in all fairness I've not pursued this far far yet -- killing the phone home program may do the job -- and the author has promised to send me instructions for a fix as soon as I send some necessary info)

Synchronize Pro X! is generally a very good -- solid, powerful, configurable and well supported. But it has some oddities and this highlights two of them:
- The author does not serve older versions of the program. This is most unfortunate given the time expiring update licensing model. If you miss an update near the end of your license period, you're out of luck.
- There is no full time-limited demo mode. This makes it very hard for people to test it (including regular customers who want to evaluate whether to renew a license after some nifty new update).

Anyway...that said, this is the first upgrade I can remember that had problems. Overall it has been a great program and I'll be happy to keep using it once this gets straightened out.