update:
after talking to a few people and doing some more testing, this seems to be a memory issue due to auto tune being badly coded from the 32 to 64 bit update. the plugin is basically still acting like an x86 plugin so crashes when the 32bit ram celling is reached.
after further testing reaper also exhibited the same issue as does studio 1.
I’m going to get on the case with Antares as it’s their problem.
cheers
marcus