IsUserAdmin returns false when UAC is enabaled in VS2010

[C++ Programming]

The following piece of code was working fine in VC++6.0 . When UAC was enabled/disabled , for an administrative user the IsUserAdmin was returning true. We are migrating VC++6.0 to VS2010. After this when UAC is enabled IsUserAdmin is returning false and when UAC is disabled IsUserAdmin is returning true. Why is this failing in VS2010 when UAC is enabled and what could be fix for this.

BOOL IsUserAdmin(VOID)
/*++
Routine Description: This routine returns TRUE if the caller's
process is a member of the Administrators local group. Caller is NOT
expected to be impersonating anyone and is expected to be able to
open its own process and process token.
Arguments: None.
Return Value:
TRUE - Caller has Administrators local group.
FALSE - Caller does not have Administrators local group. --
*/
{
BOOL b;
SID_IDENTIFIER_AUTHORITY NtAuthority = SECURITY_NT_AUTHORITY;
PSID AdministratorsGroup;
b = AllocateAndInitializeSid(
&NtAuthority,
2,
SECURITY_BUILTIN_DOMAIN_RID,
DOMAIN_ALIAS_RID_ADMINS,
0, 0, 0, 0, 0, 0,
&AdministratorsGroup);
if(b)
{
if (!CheckTokenMembership( NULL, AdministratorsGroup, &b))
{
b = FALSE;
}
FreeSid(AdministratorsGroup);
}

return(b);
}

Thanks in advance