Cubase LE 4 and MT Drumkit 2 issue

I am running LE 4 on Windows 7 64 bit and has worked without issue for several years. I have just installed the MTDrumkit 2 VST and when I play back the drum track through the USB Tascam US-122L, drum beats are dropped or missing. It sounds like a latency issue but I don’t have the common issue of playing and recording delays that most people complain of. It also plays just fine if I route it through my PC’s sound card instead of the Tascam US-122L.
Any suggestions?