Environ("username") / Dev Ashish's "fOSUserName" function return '#Name?' on some clients

I am trying to retrieve the user name (network login) of clients
running a local Access DB. We use Access 2000 / 2003 and Windows XP SP
2.

I have used 2 different ways to access this information from within
Access:
OPTION 1: Use Environ("username")
OPTION 2: Use Dev Ashish's code (http://www.mvps.org/access/api/
api0008.htm)

Both options seem to behave exactly the same for me.

But this is my problem:
On some clients I correctly retrieve the network login name and on
some other clients I retrieve '#Name?'.
On ALL clients though, if you you open command prompt and execute
'echo %username%' you get the correct answer - even on the clients
that I get the '#Name?' answer.
I suspect I have some missing reference somewhere in the clients that
can't display the username correctly but I don't know how to go about
it.

Any assistance is appreciated.