Hi Manjul

Thanks for reply I appreciate it.

I do understand it works OOTB ... it works on my Developer instance too.  But it doesn't on our own instance, and don't where to check.

If you look at my example, the duration is only one hour.  If I uncheck "Assign Across Schedule ..." the error goes away.  Even if the duration is one hour.

I think there is something else configured wrongly somewhere, I need some tips on where to check.

Thanks.