.net – the breakpoint will not currently be hit no symbols loaded

I want to debug on the customer's machine (Windows Server 2003) to track a problem, and out product is based on .NET 2.0. I want to use DbgCLR.exe to debug a file AAA.dll, what I did is:

1. install .NET 2.0 SDK on the customer's machine (to get the DbgCLR.exe)
2. copy the symbol file AAA.pdb to the same directory with AAA.dll
3. get the source file for AAA.dll

the AAA.dll will be loaded by w3wp.exe, so in the DbgCLR

1. Tools->Attach to Process, then I choose w3wp.exe
2. File->Open->File open the source file and add a breakpoint in the function which will be callled

but the breakpoint seems do no work because there is an warning icon on it and says : the breakpoint will not currently be hit. No symbols have been loaded for this document.

On my computer (Windows XP) which has the debug version of whole source code, I did nearly the same thing as above but the different is:
I attached aspnet_wp.exe to do the debug and it works

What should I do to let it work on the customer's machine?