FT-891 Frequency < > control working only intermitted

Trying to get VarAC working on a Dell laptop. Everything works (PTT, Band select, etc.) except the Left/Right (< >) Frequency buttons only work for a single press. If I select any band, the freq. changes on the rig every time. If I press the < arrow, the rig changes to the correct -750 frequency. If I then press the > arrow, the computer screen shows correct and the rig 'clicks' as if to change frequency, but the rig's screen does not move to the correct frequency. As you can see, the program is telling me it is having trouble with CAT control. I tried adding the +/- frequencies to the list, but that did not help. I am guessing the QSY U/D buttons will also not function properly. Running v.3.6.6 and CAT v2.7. Note: The program works perfectly on my desktop computer with (I believe) the same settings.