RE: Problem with DFF command not check in steel design with STAAD Pro SS6 built 20071150 (Latest built)

I can answer the part on why the limitation has been set - In general the codes have distinct load combinations for Serviceability and Strength Limit States - this is true for all the codes I can think of - Indian, Eurocode or BS. Refer to clause 2.5 of BS 5950-1:2000 for an example.

For the part of the said inappropriate message, we will advise the developers to put in a more reasonable one.