AdjustTokenPrivileges error 6 - handle invalid

Please advise why the AdjustTokenPrivileges function below always returns true, thus giving: "AdjustTokenPrivileges error 6" (ie invalid handle)?

stackoverlow is complaining that I didn't explain this enough

I don't know what else to add. I'm new to c++.

HANDLE hToken;

OpenProcessToken(GetCurrentProcess, TOKEN_ADJUST_PRIVILEGES, &hToken);
SetPrivilege(hToken,L"SeBackupPrivilege",1 );
CloseHandle(hToken);

BOOL SetPrivilege(
HANDLE hToken,          // access token handle
LPCTSTR lpszPrivilege,  // name of privilege to enable/disable
BOOL bEnablePrivilege   // to enable or disable privilege
) 
{
TOKEN_PRIVILEGES oldtp;    /* old token privileges */
TOKEN_PRIVILEGES tp;
DWORD dwSize = sizeof (TOKEN_PRIVILEGES);
LUID luid;

if ( !LookupPrivilegeValue( 
        NULL,            // lookup privilege on local system
        lpszPrivilege,   // privilege to lookup 
        &luid ) )        // receives LUID of privilege
{
    printf("LookupPrivilegeValue error: %u\n", GetLastError() ); 
    return FALSE; 
}

tp.PrivilegeCount = 1;
tp.Privileges[0].Luid = luid;
if (bEnablePrivilege)
    tp.Privileges[0].Attributes = SE_PRIVILEGE_ENABLED;
else
    tp.Privileges[0].Attributes = 0;

// Enable the privilege or disable all privileges.

if ( !AdjustTokenPrivileges(
       &hToken, 
       FALSE, 
       &tp, 
       sizeof(TOKEN_PRIVILEGES), 
       (PTOKEN_PRIVILEGES) &oldtp, 
       (PDWORD) &dwSize) )
{ 
      printf("AdjustTokenPrivileges error: %u\n", GetLastError() ); //Get error 6 here (ie invalid handle)
      return FALSE; 
} 

if (GetLastError() == ERROR_NOT_ALL_ASSIGNED)

{
      printf("The token does not have the specified privilege. \n");
      return FALSE;
} 

return TRUE;
}