I'm also running into a problem...InfoPath 2003, SharePoint 2007
(1) I have no problem retrieving list data. I fat-fingered in values into the Sharepoint List to prove this worked. It does.
(2) I created the CAML as a retrieve data connection.
(3) I added the CAML's fields to the form (via Data Source, grab field, drop, select repeating table).
(4) I created a submit data connection to my list. (https://sharepoint/_vti_bin/lists.asmx)...note for me it is https
(5) I created the ListName field with the GUI
%7B58B7B962%2D58D0%2D4368%2D8359%2D8CC5C6ECD18A%7D
translated to {58B7B962-58D0-4368-8359-8CC5C6ECD18A}
I ensured to delete the {}'s from the GUI when defining the value of ListName.
(6) I referenced the ListName and the CAML within the submit data connection as appropriate.
When I fill out the table created by the CAML Field/Name table I hit the submit button (references the submit data connection). The pop up window says it worked. However back on my list nothing was updated. Nothing was updated via the Retrieve data connection and confirmed via directly visiting the SharePoint List.
I then went back and confirmed I had the correct GUI. I then went back to my submit reference https:// and changed it from the direct subsite to the major site. The major site reference gives the SOAP error so many are getting (ie. the list doesn't exist there).
What the heck?
Another wrinkle:
I created a totally different form for another purpose for the same main site, different subsite. Within this form I figured out how to add dates from the InfoPath form (2003) into the Sharepoint Calendar. Same basic principle (GUI, etc) but accomplished via programming.
So I know within the list I'm working with I can send data (i can retrieve). I know within the website I can submit data. However I cannot get both working within this specific list?