xml.LoadData - Data at the root level is invalid. Line 1, position 1

Question

I'm trying to parse some XML inside a WiX installer. The XML would be an object of all my errors returned from a web server. I'm getting the error in the question title with this code:

XmlDocument xml = new XmlDocument();
try
{
    xml.LoadXml(myString);
}
catch (Exception ex)
{
    System.IO.File.WriteAllText(@"C:\text.txt", myString + "\r\n\r\n" + ex.Message);
    throw ex;
}

myString is this (as seen in the output of text.txt)

<?xml version="1.0" encoding="utf-8"?>
<Errors></Errors>

text.txt comes out looking like this:

<?xml version="1.0" encoding="utf-8"?>
<Errors></Errors>

Data at the root level is invalid. Line 1, position 1.

I need this XML to parse so I can see if I had any errors.

Answer 1

The hidden character is probably BOM. The explanation to the problem and the solution can be found here, credits to James Schubert, based on an answer by James Brankin found here.

Though the previous answer does remove the hidden character, it also removes the whole first line. The more precise version would be:

string _byteOrderMarkUtf8 = Encoding.UTF8.GetString(Encoding.UTF8.GetPreamble());
if (xml.StartsWith(_byteOrderMarkUtf8))
{
    xml = xml.Remove(0, _byteOrderMarkUtf8.Length);
}

I encountered this problem when fetching an XSLT file from Azure blob and loading it into an XslCompiledTransform object. On my machine the file looked just fine, but after uploading it as a blob and fetching it back, the BOM character was added.