Closed Unassigned: help!!! MAPILogonEx question!!! [16458]

Hello!

Could anybody help me with this problem:

I trying to write NT Service that works with MS Exchange Server. When I
call
MAPILogonEx() it returns with -2147221231 (ClassFactory cannot supply
requested class). the Service is executed under the local system account, but i call MAPILogonEx with administrator account, it success, What is the problem, what am i doing wrong?

here is my code:

HRESULT hRes = ::MAPIInitialize(NULL);

ULONG ulFlags = MAPI_EXTENDED | MAPI_ALLOW_OTHERS | MAPI_NEW_SESSION |MAPI_USE_DEFAULT;

hRes = ::MAPILogonEx(
0,
NULL,
0,
ulFlags,
&_lpMAPISession);

Thanks in advance,