If anyone cares: The error returned by ADSI when the NT account does not exist is -2147022675. To make sense of ADSI errors try this:

1. Convert num to Hex -2147022615 = 0x800708AD
2. Strip top 4 bytes = 08AD
3. Convert back to Dec 0x08AD = 2221
4. Look up this error with NET HELPMSG 2221

code:
H:\temp>net helpmsg 2221

The user name could not be found.


EXPLANATION

You specified an unknown user name.

ACTION

Check the spelling of the user name. To display
a list of the users in the security database, type:

        NET USER
cj