Using setInfo() in C++ results in E_ADS_INVALID_USER_OBJECT

I am trying to use the setInfo() function in C++ to commit a few changes to a user's e-mail field in Windows AD. I am making a DLL that gets exported to a Windows service. But setInfo() keeps returning:

E_ADS_INVALID_USER_OBJECT

Everything works fine if I compile the EXACT same code into an EXE and run it in a command line. But when the DLL is exported, and setInfo() is called, it returns the above error. This is a portion of my code:

IADsUser *pUser = NULL;
RESULT hr = CoInitialize(0);
VARIANT var;
hr = ADsGetObject(L"LDAP://CN=Foo Bar,CN=Users,DC=mydomain,DC=com", IID_IADsUser, (void**) &pUser);
//hr = ADsOpenObject(L"LDAP://CN=Foo Bar,CN=Users,DC=mydomain,DC=com", NULL, NULL, ADS_SECURE_AUTHENTICATION, IID_IADsUser, (void**) &pUser);

VariantInit(&var);
V_BSTR(&var) = SysAllocString(L"foobar@email.com");
V_VT(&var) = VT_BSTR;
hr = pUser->Put(CComBSTR("mail"), var);
hr = pUser->SetInfo();

I am able to bind with LDAP successfully, the binding works also with this:

ADsOpenObject()

When I add the domain Administrator credentials in ADsOpenObject, setInfo() works.. but I do not want to use username/password for this. Is there a way to use setInfo() in a DLL without providing the credentials in code?

Also, the IADsUser Get function works without providing domain admin's credentials. Is it a read/write issue?

If you don't explicitly provide a username and password when you bind to the AD, Windows uses the security context of the process to log in. For a service running as local system or as network service, this means that it logs in using the computer's AD account.

If you change the permissions within the AD to grant the necessary access to the computer account, it will work. (The username for the computer account is the computer name with a dollar sign appended.)