>>>>Can be any .when() event up the return stack... does your error routine leave a stack dump so you can see how it got there?
>>>
>>>Ah but I haven't been able to repro the error since (I restarted VFP assuming it had got its knickers in a twist).
>>
>
>>What, your error catcher doesn't log?
>
>No, just reports errors (ahem! don't get errors) :-)

Then, sorry Sherlock, no trace left on the scene. Use deduction.