Hy ! And I'm new in this field. For 6 days I try to understand this process . I recieved same error for another xp machine. I resolve this problem ...
On the computer server where you build COM+ you need select DLL and TLB files, and go to 'Properties' for "name" server, click 'Security' tab and select for 'Authentication Level for Calls' : 'None' option.
And I do something like that and the server running (for no problems).
I work with VFP8 and a tested above on two xp machines .

Goodluck