I just experienced the same issue. The Virus Control plugin in a Reaper project saved on Mac wouldn't open in Windows (plugin not found). Replacing the following strings in Reaper project file (.rpp) with a hex editor solved the problem.
Mac <VST "VST3i: Virus TI (Access Music Electronics GmbH) (4->6ch)" "Virus TI.vst3" 0 "" 840036114{B49F90D9735F4305AC5397BE8958CD31} ""
Windows <VST "VST3i: Virus TI (Access Music Electronics GmbH) (4->6ch)" "Virus TI.vst3" 0 "" 1613304334{D9909FB45F730543AC5397BE8958CD31} ""