If you're making snapshots from SQL Compare 9, you need the SQL Compare 9 binaries in the SDK to read it back. Problem is there is no v9 of the SDK, so you can't buy an upgrade at this point.
You may want to wait a few weeks until the SDK 9 upgrade is finished going through testing. There are a few problems at the moment with using the v9 binaries - first of all you have to get them from the SQL Data Compare distribution because SQL Compare is merging the engine into the executable and second, it's error-city when I try to compile the SQL Compare Engine code samples with the v9 engine.
Looks like it requires .NET 3.5 for a start, and also there are lots of compiler errors around the WriteToFile stuff: I would assume they've rearranged the API again there. If you want to give it a try with the SQL Data Compare version of engine, be my guest, but I don't have any answers at this point if your code doesn't compile any more.