Parsing through IStream with XmlLite - resetting reading position with seek() doesn't work

I am calling a function several times, that parses through my xml file to get some data. When I call the function the second time, of course the reader still is in the position he ended up before, as it gets its input from the IStream class.

I now do this:

LARGE_INTEGER reset;
reset.QuadPart = 0;
if (hr = pFileStream->Seek(reset, STREAM_SEEK_SET, nullptr) != S_OK)
    return hr;

at the beginning of the function to set the reading position at the top of the file. Unfortunately it doesn't work. There is no error, nor a warning.

Any Ideas what I am missing here?