Invalid XML characters
ADO.NET replaces invalid XML characters found in custom field names and parameter names. The
      invalid characters are replaced with "_xNNNN_" where "N" is
      a hexadecimal code that equals the original character.
This XSD shows how the node for a custom field named “BAD%FIELD$NAME”  is
      configured with the hexadecimal numbers for “%” and “$”. The invalid XML characters % and $ in
      the custom field name BAD%FIELD$NAME are converted to hexadecimal equivalents”_x0025_” and
      “_x0024_” in the XSD.