RAM Connections - Load combinations

I am designing the connections using RAM connections. When I switch from RAM structural to RAM connections I am seeing the warning " The analyzed load cases have changed and load combinations should be regenerated".

However, under add/edit, there are combinations already generated C1, C2, C3, etc...

But because of the warning I generated the load combinations again and these new load combinations are added as D1, D2, D3 ...... etc. 

What is the difference between load combinations called as 'C' & 'D'? and is it necessary to generate load combinations again because of the warning.?

Also, connections are analyzed for both C & D combinations in the report.