Error I don't understand

Hi all ...

Got another problem with trying to program with libwww ...

I am writing a proxy and am using HTLoadToStream to send the result 
from the server to the client.....

but I am having the following error ...

WWW Alert:  Fatal Error 501 command not Implemented Can't convert from www/mime 
to www/present

I have already setup the conversion by the following :
        request = HTRequest_new();
        if (!request->conversions)
            request->conversions = HTList_new();
0.0, 0.0);


What am I doing wrong ?

Thanks in advance

Tommy Tsui