The upgrade went through without issues, the project builds properly, all the connections test correctly, etc. However, after starting the package (which consists of several Transfer SQL Server Object Tasks), the first two succeed and the third fails with:
[Transfer SQL Server Objects Task] Error: Execution failed with the following error: "Cannot access property IsExternal.This property is not available on SQL Server 2008 R2.".
Is there a way to get a more detailed error, if nothing else? As is, I don't even know where it's trying to find this property.
Packages developed with SSDT will not work on any server on or before SQL Server 2008 R2. For SQL Server 2008 R2 and prior use BIDS. I know it's a pain but at least SSDT is now readily available (included with VS 2013+) compared to BIDS (if you have modern servers).