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.)

There are no addresses available for this application

After creating a Business Data Connectivity Service Application in SharePoint 2010 I wasn’t able to access the service application with the BDC models, external systems and external content types.
I tried to deploy a Visual Studio Solution by hitting F5. The error message I received was: "Error occurred in deployment step 'Add Solution': There are no addresses available for this application.” Clicking the BCS under "Manage service applications" got the same error.
Solution:
Check that the service under "Manage services on server" is running. If the error occures despite the service is running, restart the IIS with "iisreset".

BCS: Association Error

You are developing an association between BCS entities. You encouner an error like:
Exception handed to HandleRuntimeException.HandleException System.InvalidOperationException: The Association with Name 'SomethingAssociationNavigator' expects '1' EntityInstances (External Items) as input, but '0' were supplied.
Maybe you have defined the finder method of the entity but you missed the specific finder method or you defined a specific finder method but it has a faulty parameter definition.

BCS - add item form for creator method not working

You have created a BCS model, added a creator method to it but it is throwing an Runtime Error. In the logfile you find "SPException: Unable to find the default new form for list"

A probable reason for that error is the following. You created the model only with a ReadList and ReadItem method. Then you created a list in SharePoint and tested that functionality. Then you added a creator method and used the previous created list to add an item. That does not work because the list was provisioned without the "new form". Just delete the list and create a new one. The "new form" for the list should show up as expected.

Access denied. You do not have permission to access this content

You have created an External Content Type in SharePoint Designer 2010 with the authentication mode "User's Identity". When you create a list and want to access the data in your portal, you get the error message "Access denied. You do not have permission to access this content" or "Access denied by Business Data Connectivity".

You need to set permissions in Central Administration under "Manage Service Applications" in the "Business Data Connectivity Service Application". Click the BCS service and configure the permissions in the context menu of your ETC.

Also the user needs permissions in your external database.