XmlException: The data at the root level is invalid. Line 1, position 1.

I have tried to fins anything about this on Internet, and do get some hits. However, I don't seem to be able to figure out what is wrong. Anyone that have an idea?

The data should be ok. It starts like:
<?xml version= ......

Code:

           System.Text.ASCIIEncoding encoding = new System.Text.ASCIIEncoding();

            byte[] bytesin = encoding.GetBytes(msgin);
            ProtocolHeader protocolHdr = ProtocolHeader.ReadProtocolHeader(bytesin, 0, msgin.Length);

            MemoryStream hdrin = new MemoryStream(bytesin, Convert.ToInt16(protocolHdr.ProtocolHeaderSize), msgin.Length - Convert.ToInt16(protocolHdr.ProtocolHeaderSize));
            XmlReaderSettings xmlReaderSettings = new XmlReaderSettings();
            xmlReaderSettings.IgnoreWhitespace = true;
            XmlReader msginReader = XmlReader.Create(hdrin, xmlReaderSettings);
            


            while (msginReader.Read())
            {
// ...
            }

Perhaps it isn't an ASCII file at all, and it ran into this at the start of the file.
http://en.wikipedia.org/wiki/Byte_Order_Mark

Hmm, slightly embarassed. I think I found the error. I started one character to late. I skipped the <.

Thank you anyway. Sometimes one just have to express the problem to realize what actually is the bug.