RFCOMM: Windows Mobile 2003 - Virtual COM Port - ERROR_DEVICE_IN_USE

I'm developing an application (Pocket PC 2003 / Windows Mobile 2003) which should establish a RFCOMM Bluetooth connection to a bluetooth-server-device. ( A serial interface for an older non-bluetooth version of this device already exists. PPC is the T-Mobile MDA )

So i checked the scanty microsoft documentation and found out, that it is possible to create a virtual com port with
RegisterDevice(L"COM", index, L"btd.dll", (DWORD)&pp).

With WSALookupServiceBegin(...) and WSALookupServiceNext(...) it was possible to detect the BT_ADDR needed for the PORTEMUPortParams (see above -> pp ) device parameter.

But RegisterDevice always fails with SystemError:ERROR_DEVICE_IN_USE (The device is in use by an active process and cannot be disconnected.) - Then i checked the "HKLM\drivers\Active" Key in my PPC registry and found out, that there is no service using COM 4, 5 or 6. But this Ports also generate this error message.

Interestingly enough the "btd.dll" is not yet loaded. So i guess my PORTEMUPortParams structure isn't the error source.

The sample source code supplied with Windows CE Evaluation Edition seems to do exactly the same.

Maybe I could have forgotten to implement several important gimmicks. Or maybe there is another way to connect with a RFCOMM bluetooth device.

Thanks in advance.

Here is the source (without catching any errors :)

/*+++++++++++Startup WSA+++++++++++++++++*/
WORD wVersionRequested;
WSADATA wsaData;
wVersionRequested = MAKEWORD( 2, 2 );
WSAStartup( wVersionRequested, &wsaData );

/*+++++++++++++Search for my device++++++++++++++++*/
INT iResult = 0;
LPWSAQUERYSET pwsaResults;
DWORD dwSize = 0;
WSAQUERYSET wsaq;
HANDLE hLookup = 0;
memset (&wsaq, 0, sizeof(wsaq));
wsaq.dwSize = sizeof(wsaq);
wsaq.dwNameSpace = NS_BTH;
wsaq.lpcsaBuffer = NULL;

WSALookupServiceBegin(&wsaq, LUP_CONTAINERS, &hLookup);

union {
CHAR buf[5000];
SOCKADDR_BTH      __unused;
};
pwsaResults = (LPWSAQUERYSET) buf;
dwSize  = sizeof(buf);            
memset(pwsaResults,0,sizeof(WSAQUERYSET));
pwsaResults->dwSize      = sizeof(WSAQUERYSET);
pwsaResults->dwNameSpace = NS_BTH;
pwsaResults->lpBlob      = NULL;

WSALookupServiceNext (hLookup, LUP_RETURN_NAME | LUP_RETURN_ADDR, &dwSize, pwsaResults);
// Real device name is found ... pwsaResults->lpszServiceInstanceName;

/*+++++++++Now trying to register the virtual COM Port+++++++++++++++*/
PORTEMUPortParams pp;
memset (&pp, 0, sizeof(pp));
pp.channel = 0;
pp.flocal = false;
pp.device = reinterpret_cast<_SOCKADDR_BTH*>(pwsaResults->lpcsaBuffer->LocalAddr.lpSockaddr)->btAddr;
//the detected BT_ADDR
memcpy(&pp.uuidService, &CLSID_NULL, sizeof(GUID));
pp.uiportflags = RFCOMM_PORT_FLAGS_REMOTE_DCB;
int port = 4; //or anything else like 1..4,5 or 6..9 | Limit is 9 i think
HANDLE bth = RegisterDevice  (L"COM", port, L"btd.dll", (DWORD)&pp));

/*++++++++the result+++++++++++++++++++*/
//bth == 0
//GetLastError () == ERROR_DEVICE_IN_USE :(