So that tells me that not everything is the same. What versions of mach 3 are you running?
Do this.
On new computer copy the UC100 DLL file from the C:/mach3/plugins folder to a memory stick.
Rename the C:/mach3 folder on new computer to say C:/mach3 old
On the old computer copy the entire mach 3 folder (yes all 200+ meg of it) to a memory stick.
Copy this to the C drive of the new computer.
So on the new computer you have a C:/ mach3 and C:/ mach 3 old directories.
Copy the UC100 DLL back into the C:/mach3 plug ins directory.
Go and download .062 version of mach3, not the 66.
ftp://machsupport.com/Mach3/download and install with default values. it will overwrite the core files of mach but not any settings. This also gives you a stable version of mach that works with USB motion controllers.
now you should be set with exactly the same setup as on the old computer. As its the old computers files.
When you open mach for the first time, you may have to reset device selected and restart mach so you can choose the UC100