Cannot open old project in 4.12

Just downloaded 4.12 and I can no longer open my old project. This is the error that I am getting.

Assertion failed: InComponent->InstanceReorderTable.Num() == InComponent->PerInstanceSMData.Num() [File:D:\Build++UE4+Release-4.12+Compile\Sync\Engine\Source\Runtime\Engine\Private\HierarchicalInstancedStaticMesh.cpp] [Line: 756] &nl;&nl;