To solve the “Could not determine storage version; a valid storage connection or a version hint is required” when updating the data sources in Microsoft Ligthswitch, you need to modify the Data\ApplicationDefinition.lsml file to match your ConnectionStringGuid with the ServerGenerated\Web.Config.
Notice the green boxes in the above image. It is the ApplicationDefinition.lsml file with the ConnectionStringGuid property. The value of the property should match to the Web.Config file as seen in the image below.
I really don’t know why these things happen, but it happen to me in a middle of a busy day.