I'm running into the same issue.
I've created a very simple Win-32 program that does a read-only (dieselnutjob, thanks for your hint) of the same key as ffejrobins30 used.
On my Vista-32, N2K VM, Vista-32 VM, Win7-32 VM - I get the expected GUID.
When I run this on my Win7-64 system (real machine, not a VM), I get an empty string.
I have verified that the regedit path and parameter name are identical.
0.9.31-33481-2.5-1-win32, on a Win7-64 system