Steel Roof Truss Design.

Dear All Expert,

I am trying to design simple steel roof truss using  British Code BS5950.

I also trying to use steel design to check or design my member size whether sufficient or not to handle the load.

However I getting some error during analysis for M73, I selected all other members as pipe under British section database except for member M73(Purlins) I select the section as Lysaght Cold Formed Channel which are not under British section database that why i getting this error right?  

Is that a way to design it based on two different section database that I selected?. 

Besides that, I notice that my M1 fail at Comb.Axial & Bend Chk but when I go Select>> By Specification>>All Failed Beam M1 is not selected by Staad so whether M1 is pass or fail?

After that, I select Member design>>Perform Group Design>>Member Selection(Single Step Design) my section for M1 become PP1393.2 but now the Comb.Axial & Bend Chk is pass now, do I need use this PP1393.2 section as my final section selection instead of PP763.2 just because it pass at Comb.Axial & Bend Chk??

Thanks.

Roof Truss.std