I'm trying to parse and validte an existing XML-file by parsing it and then validating it through XmlOptions. this works perfectly until I try to do the same thing from a different thread. Then I suddenly get a "cvc-elt.1" error. This error states that the xml is missing some kind of declaration in the schema file. but this is not the case because the same code works perfectly in a single-threaded environment. Can somebody explain what causes this error and how to solve it?