I can't find the old thread that gives the info you need on this. It is possible to remedy the problem by altering the permissions on the registry key(s) that are giving the problem, but the secondary problem becomes finding which keys those are.
I would just log in as Administrator, open Regedit, navigate to this key:
HKEY_LOCAL_MACHINE\SOFTWARE\JRiver
And then change the permissions on that whole key so that Limited Users had full access to it. To do that, right click the key in Regedit, select Permissions, find the Users entry in the list that appears, then check "Full Control" and click OK.
Then, log in as Limited User again, and see what happens. Hopefully, that will be enough. But if I'm wrong, and the affected key(s) lie elsewhere, it will take more digging.
At that point, you could download and run
Sysinternals Regmon, and try using it, while running MC, to see which registry key(s) MC is hammering. But this poses yet another problem--Regmon normally requires Administrator privileges to run, but you need to test as a Limited User.
If you're running Win2K or WinXP Pro, you can go into the "Local Security Settings" applet (find and run secpol.msc), and give the Limited User the ability to "Load and unload device drivers", and then reboot. (Be sure to undo this security policy change later, if you make it.) Then, Regmon should work, I believe. With WinXP Home, I don't think there is any way to accomplish this so easily.
Sorry, I can't remember exactly how I solved this, but hopefully the first idea above will suffice.