I often received a web.config error message in EdiForm of an External List using a custom BCS model with my own implementations for Updater method in .NET assembly.
Trace logs showing an error message as “Application error when access /Lists/***/EditForm.aspx, Error=The data source control failed to execute the update command. ***** at Microsoft.SharePoint.WebPartPages.DataFormWebPart.UpdateCallback”
This was frustrating as there are no details about this error, debugging using VS2010 did not help either.
So after weeks of trail and error i found out that one of the Data Type was defined as “String” in BCS Entity model but its actual Data Type should be “Character” as defined in LINQ to SQL object.
SharePoint BCS model is very stringent on Data Types and not very specific when reporting the error messages. Also it is important to make sure that Identifier field must have Updater Field be set to True in the Updater method.
