I'm one of the few that didn't have problems. I have UAC disabled.
I think UAC is blocking a registry change made by the UOAssist patch, the very same one everyone is manually changing. Those entries do not exist for me.
Instead of ...
HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\Origin Worlds Online\Ultima Online\1.0
...followed by the entries you guys are seeing.
I have....
HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\Origin Worlds Online
All that is there is the following:
(default)
HarvestStageNew
LastHarvestTIme
UniqueInstanceId
There are no values set for any entry.
It looks like the patching process is supposed to clear all of the entries that everyone is seeing, but UAC is somehow preventing that from happening. Again, I suspect it is simply a matter of giving the proper permissions to all of the .exe files (so that they have permission to clear out these entries).
So, either turning off UAC or giving full Admin permissions to every .exe involved should fix Win7 users problems. But that doesn't address the issue of what to do if those entries are still there, as I don't see them on my machine. Perhaps just simply attempting to patch normally will work. Can't test it myself.
Good Luck!
EDIT: For those of you that do not know, UAC is specifically designed to prevent one application from altering another, including registry entries. It appears that either UOAssist did exactly that--attempted to modify the registry for UO--and UAC prevented it from happening, or, a change in one of the UO executables (probably a temporary change to facilitate installing the new Patcher) led to UAC preventing it from clearing those entries when it shouldn't have. In that case, the UO devs should have anticipated this and gave their applications permission to properly clear the old/temporary entries. Maybe that first error in the DOS window is actually a result of just that--the new application didn't have permission to alter the old ones. Whew! That was a mouthful. I'll shut up now.