3 machines involved.
Windows 7 64-bit w/2 hard drives (Machine A)
Windows 7 32-bit notebook (Machine B)
Windows XP, SP3 w/2 hard drives (Machine C)
All machines can access each other's C drive.
Both Windows 7 machines (A & B) can access 2nd drive on XP machine (C).
Neither B or C can access 2nd drive on Windows 7 machine (A).
Message: ...drive is not accessable. You may not have permission to use the network resource.
Followed a similar thread and checked all permissions locations.
All permissions show shared in every way possible.
Had no success setting up Homegroup to do it, so removed it.