Following are some of the reasons why your Visual studio will not hit break points.
1) Project is not fully built: For this you clean your solution and make a rebuild.
Still if it is not hitting, right click on the break point, Click Location and
in the dialog that opens, Check the check box (Allow the source code to be
different from original version)
2) The break point is not in the code execution path: For this, ensure you have
put the break point in the right place. Put the break point at the starting of
the event/method, Should not be inside a condition or elsewhere. Also, put the
break point immediately in the Page_load.
3) Debug is not enabled in the application: In your web.config ensure that
following is present:< compilation debug="true"/>
4) You are trying to debug unmanaged code:
1.From the project properties page, in the debug tab, make sure we tick the
checkbox, "Enable unmanaged code debugging"
2.From the menu Tools->Options, navigate to Debugging node, uncheck the
checkbox "Enable Just My Code".
3.Make sure you provide the correct pdb files of the VC6 executable of dll.
Please see the below links if you still have issues: