Varispeed starting issue

I have created an issue that I don’t know how to recover from. I last use by BP varispeed clone in back gear with the speed wound up to the top end. It’s cold in my workshop and I can’t now get the mill running as the belt is slipping at the the motor end. I think the situation is like trying to pull away in a car in top gear. The directions clearly states
not to wind the varispeed down when when it’s not in motion. I tried it in neutral but it made no difference the spindle is free anyway, of course the top end of the drive still needs to be rotated. I can’t rotate the spindle in gear due to the gearing. I can see the belt through a side cover and it’s not moving much on start up and I can hear an unusual noise. I don’t leave it running for more than a few seconds for fear of damaging the belt. The motor is on a VFD and has always worked flawlessly, the VFD is showing no errors.

So Assuming my diagnosis is correct I’m looking for a way I can fix this simply without a major strip down. If that’s needed I’ll replace the cone bushes.

Thanks

Tony