How can I use a DLL-Funktion that returns a float?

I'm using an extern DLL in my applicaiton.
To use the DLL-function I use this wrapper:

public static class OTRDecoderSDKWrapper
{
[DllImport("decoderdll.dll")]
private extern static int Decodieren(string aQuelle, string aZiel,
string aSchluessel, ushort Pause);
public static int decode(string aSource, string aTarget, string aKey,
ushort aDelay){
return Decodieren(aSource, aTarget, aKey, aDelay);
}
public static int decode(string aSource, string aTarget, string
aKey){
return Decodieren(aSource, aTarget, aKey, 0);
}
[DllImport("decoderdll.dll")]
private extern static float Status(ref byte Vorgang);
public static float getStatus(ref byte aOperation){
return Status(ref aOperation);
}
}

docde() decodes a file - this is done in a Thread.
getStatus() returns a percentage value of the decode()-Status.

My problem is, that getStatus() everytime returns 0.
I found this thread
http://www.dotnet247.com/247referenc...48/240427.aspx but that is
no option for me, because I don't have the DLL-sources.

Is there a way to use the getStatus()-function in my c#-application?

Kind regards

Markus