Sonar crashing when applying 'midi synch' and running Sonar as slave

I'm trying to midi synch an external sequencer to Sonar but am having real issues with time drifts.
A fellow forum member suggested I run Sonar as the slave and set clock to 'midi synch'
This is causing Sonar to crash.
Any ideas what's going on?
p:s (I've tried both 'audio' and 'internal' in the clock setting with Sonar as master,but timing discrepancies prevail)