InfoPath Dev

 I have a submit data connection set up to take all of the XML from a secondary data source to be input into a string parameter of a web service.

 This works if using InfoPath Filler but when I choose to edit the form inside of a web-browser, I get the error, "There has been an error while processing the form" without any other informational messages. 

This is the Xpath set up in the "Field or Group:" setting, /dfs:myFields/dfs:queryFields.

 I have converted this data connection to a Data Connection library inside of SharePoint.

 I'm wondering why it works with Filler but not when inside of a web-browser.

When you get that error message in the browser, does it provide a correlation ID? If so, would you be able to fetch the associated error from the SharePoint logs?

 No, there's no additional information provided in the error box, as I would expect.  Just the message and two buttons, "Try Again" and "Exit Form."

I see. Does the error occur when you try to execute the data connection, or at some other time? Does the form use any custom code? Would it be possible to open up the SharePoint logs immediately after the error happens to see if you can find some related error?

Error occurs at the execution of the data connection.  (The error does not occur when I choose to send the main data source XML in the submit data connection.)

This form does not use custom code.

The event viewer logs do kick out a form postback error, "Form ID: urn:schemas-microsoft-com:office:infopath:AimTest:-myXSD-2013-05-17T15-01-30, Type: KeyNotFoundException, Exception Message: The given key was not present in the dictionary.)"

(I just recently found that error message.)