Thanks Ernesto, the error only shows up when I try to execute the SaveToSharePoint command (on change for the Attachment field). I've used this method successfully in other forms.
I tried to attach my file using the Options tab, but my file is 139k and the upload is limited to 128k. If you can send me an email address I can send it to you that way.
Here is my Command. It's set to run when the Attachment field changes.
concat("SaveToSharePoint /url=http://devsp01/sites/ewlc/Form%20Attachments /xpath=/my:myFields/my:CompletionRTCDataInputSection/my:RepeatingSection/my:RepeatingSectionOtherDocuments/my:OtherDocuments /name=danTest1" /overwrite=true /dsnamews=CopyIntoItems")
(I added the /dsnamews data connection and parameter as a test, but it didn't change anything.)
I also tried the GenerateGuid command on a button and I get the same error. I attached a screen shot of that setup.