Ok, I'm not related to NCH, but found a way to restore my data.
First, locate the folder where you created your back-up. Then, look for the data folder for the re-installed program (mine was under C:/documents and settings/all users/application data/NCH software/expressinvoice ) You may have to change the permissions for that file folder under the security tab of the properties.
Next, I deleted all of the contents in the expressinvoice folder.
Then, I copied all of the sub-folders and data files from my back up folder to the expressinvoice folder.
Then restarted the program, and voila - everything was restored.
I realize this is a bogus way to have to do it, and the NCH should jump up and create a proper restore function, but hey, at least I'm back up and running!
Regards
Dave