From IDF support:

The file you need to delete is "identityinfo.dat" and is located here: 
Vista/2008/7 -> C:\Users\[USERNAME]\AppData\Local\Identity Finder\identityinfo.dat 

2000/XP/2003 -> C:\Documents and Settings\[USERNAME]\Local Settings\Application Data\Identity Finder\identityinfo.dat 

Where USERNAME is the name of the user account that needs a password reset.