Please help me How to set Global signal?

[Altera_Forum]

Quartus II 9.1 design assistant said "Critical Warning: (High) Rule C105: Clock signal should be a global signal. (Value defined:25). Found 3 node(s) related to this rule." I turn off Auto Global Clock,Auto Global Memory and Auto Global Register in Fitter setting. And set the three pins as Global Signal ON and Auto Global Clock ON.But this time Quartus II said" Warning: Assignment for entity set_instance_assignment -name GLOBAL_SIGNAL ON -to USBCLK -entity A2 was ignored" and still said"Critical Warning: (High) Rule C105: Clock signal should be a global signal. (Value defined:25). Found 3 node(s) related to this rule." 

 I just compiled the same project by Quartus II 7.1.No warning. Maybe it is some bugs of Quartus II 9.1？   Could anybody tell me why?   Thanks!

[Altera_Forum]

What's the source of the clock signal? 

A pin? If so, is it a dedicated clock pin?

[Altera_Forum]

--- Quote Start ---  What's the source of the clock signal? A pin? If so, is it a dedicated clock pin?  --- Quote End ---      It's a dedicated clock pin.