How do I Debug a .net DLL used by an Asp.net app?

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Hi, I'm trying to debug an asp.net DLL from an asp.net app.
I'm successfully calling (though not debugging) the dll from one page, and a
call to the DLL fails on another page with
Object reference not set to an instance of an object.

Hence the need to debug.

I've created the DLL in debug mode, and have coppied both the .DLL and the
..PDB files into the bin diectory of the asp.net app.
I've go both the DLL project and asp.net app in the same solution, if that
helps / hinders.

What am I doing wrong?

Many thanks.

(Asp.net 1.1)

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RE: How do I Debug a .net DLL used by an Asp.net app?

Working now.
Wish I knew what I did - just refreshed (as I had done, though added a new
interface)