[RESOLVED] What does 'No Source Available' mean ?

I'm trying to debug a project which has gone sick on me... Probably due to some 'weeding' in the Registry Patch.

When I run the project all seems to work except that the texts in several TextBoxes don't change. So, using VB 2010 Express I opened the project and clicked the 'Start Debugging' button (little green triangle) and the project ran exactly as it does when I run it from the desktop button, i.e. no change of text.

So I tried using the single step f key (to start the debug) and it opened a new page:

[No Source Available] (Tab)

No Source Available
There is no source code available for the current location.

To investigate further, try one of these options:
Browse to Find Source

Call stack location:
mscorlib.dll! System.Runtime.Hosting.ApplicationActivator.CreateInstance(System.ActivationContext activationContext, string[] activationCustomData) + 0x66 bytes

(End of page)

I've checked and found that mscorlib.dll is in C:\Windows\System and also in System32.

I don't understand what the 'Call stack location:' is telling me, or what to do about it.

Poppa.