Gong,
from what you are describing, it appears you might have encountered the situation described on this KnowledgeBase
It discusses potential issues when opening a 2.0.1 sequence with a previous version of TestSTand. Problems are due to the fact that new Types were introduced with TestStand 2.0.1.
If this does not solve your problem, I suggest you explain in better detailed way what messages pop up from teststand when opening a sequence. You could also attach a screenshot, that would make things a lot easier.
Regards,
AlessioD