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data at the root level is invalid. line 1 position 1

Details:

Data imports or data models choking.

Error Message:

data at the root level is invalid. line 1 position 1

Solution 1:

Your models don’t match up correctly.

Solution 2:

The hidden character is probably BOM.

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.

Resources: https://stackoverflow.com/questions/17795167/xml-loaddata-data-at-the-root-level-is-invalid-line-1-position-1