Bob,
This, from the web site, looks like your problem. You can get the patch or latest version there.
Alan WA4SCA
5. Patches
a. SatPC32/Wisat32 patch The ZIP file that can be downloaded with the link below contains revised SatPC32.Exe and Wisat32.Exe files (English demo version for North American users).
The files that come with the 12.8a setup file cause a math error (message: "Ungueltige Gleitkommaoperation" = "Invalid floating point operation") in the following case: a. In menu "Optons" the SGP8SDP8 model has been chosen (the SGP4SDP4 model works flawlessly). b. An element in the Keplerian data set ("bstar drag term", data line #1, col. 54 - 60) contains the value 0. Presently (Dec. 2009) that is the case with data sets for HO-68.
Selecting the SGP4SDP4 model fixes the problem also. The results of both models are of equal precision.
Further, the revised SatPC32.Exe file fixes the following error: When the program's "Priority" function automatically switchs to a satellite it will set a possible converter or transverter offset to 0. So, the radio will not be tuned to the required downlink or uplink frequency.