Data Source Conflict

If you are developing BCS solutions in Visual Studio, you might have experienced the following error when you attempt to create or update a new item in an external list:

DataFormWebPartException: Data Source Conflict: Your changes conflict with those made concurrently by another user. Refresh the form and submit your changes again.

Solution: In your Visual Studio 2010 BCS project, find the Create or Update method that's failing. Verify that each of the fields in your input type descriptor have the Creator property (for the Create method) or Updater property (for the Update method) set to True.
Note, this property should not be set to true for the identifier field if the LOB auto generates the value. You also need to delete and re-add the external list before the changes take effect. (Because the object definition of the external content type is saved in the existing list and does not change when you update the BCS model.)

Debugging SharePoint Solutions

You are using Visual Studio 2010 on a SharePoint 2010 site and get an error when hitting F5 to begin debugging....
The debugger may fail to start and complain that the web.config could not be loaded with the error message: “Could not load the Web.config configuration file. Check the file for any malformed XML elements, and try again. The following error occurred: The given key was not present in the dictionary.”
Make sure the URL assigned to the Default zone for the Web Application’s Alternate Access Mappings matches the Site URL of the SharePoint project in Visual Studio. Using one of the other zones (like Intranet) for the URL will not work. The Default Zone and the project’s Site URL need to match.