If you aren't programmatically creating a sequence file in .NET you might be getting the out of memory error for a different reason. If you are using XML format you are more likely to run out of memory as that format requires more memory to save.
That said, if you using TestStand 2012 or higher, you can call the engine API: engine.DoDotNetGarbageCollection(0); or use a dotnet code module, or call GC.Collect() directly using the .NET adapter.
-Doug
