Thanks to those that gave advice. Upon viewing the *.mdb file that is created by The Station Program, I noticed that there was no Mir definition in the database even after loading elements several times. After moving the keps for Mir to a different place in the file, I reloaded the elements and it appears to be working.
Paul, is this a known issue with The Station Program? Is it supposed to work this way? I can't find anything about this in the manual other than how to set up the program for Mir/SAREX missions.