strange security problem

[Peter Foley]

I want to run asp.net under ID A and web service S under ID B (for logging
reasons).

However as soon as web service S accesses any COM object the web service
infinitely loops (from FileMon it seems to be continually reading
WinLogon.dll).

If I run service S under ID A or run asp.net under ID B (i.e. they match) no
problems!

Any ideas?