From and I get the impression it should just be a drive letter. But it should certainly be exactly the same as you typed when running the wizard on the 'old' PC.

I googled the error message
and found a lot of helpful links, like

From what I read there you should take care that:
a) the drive letter in the new configuration is the same as in the old one
b) you point to the parent folder of the USMT2.UNC file

If it really doesn't work, you've lost your settings. But you might have your data on some other backup?