Access Violation -> Error address not found

What does it mean if a program throws an access violation, but when I
try to find the code associated with the error, I get the message
"Error address not found?"  

My assumption is that the CPU has run off into data space, but I'd
think NT would give a fault before that happened.  Does the NT memory
model not distinguish between code and data?

Thanks for any insight,

- Eric Zager