improvisator wont play in cubase 6.5

Does anybody know why improvisator will not trigger a vst ( such as Nexus ) it works fine in Cubase 5…improvisator will play in Cubase 6.5 with it’s internal synth but if I rig it up as in Cubase 5, Nexus instrument track then improvisator selected on f11 with a midi track then improvisator output goes to nexus input to trigger Nexus, as i said…works fine onC5…is it because i’m on 64 bit with C6.5 ? and if so why would that effect the midi bus connections ? hope some bright spark out there can put me right…thanks, Kevin