You're missing a my: from your frowid line, but since the xmldata variable is referencing a single node, your code is set up to place new values into that field every time the loop iterates until the value from the last loop is placed there and the loop ends. Is this what you mean to do? The data source where you're assigning the values seems to be different from the one you're submitting.
For the submit code, you should be using thisXDocument, not XDocument, and Submit() should be capitalized.