Debugging doesn't stop in my breakpoint

Hi,using visual studio.net 2005 full version and after setting up my breakpoint(eg.Page_Load) and the Start up page and when Start Debugging(F5), the process doesn't stop in my breakpoint. then I opened the same project, same breakpoint and start up page in VS 2008 express edition everything worked ok and the process stopped in my breakpoint!!!!?So, is the something to be set in my VS.net 2005 full edition? Thanks   
 
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