ThisApplication_Startup - can't stop at breakpoint.

I am trying to debug a VSTO outlook add-in (compiled in debug) app but can't get the debugger to stop in ThisApplication_Startup(). The debugger displays a warning saying "this breakpoint won't be hit. No Symbols have been loaded for this document"

Yet I compiled it in debug and set the debug options to load outlook as the external EXE program.

Whst am I doing wrong

Thanks in advance...