Hello,
There are two KnowledgeBase documents that talk about the possible reasons for memory leaks with TestStand and LabWindows/CVI. Those documents will give you some ideas.
http://pong.ni.com/public.nsf/websearch/EFA67CCC5836BC8586256BE60062C3D8?OpenDocument
http://digital.ni.com/public.nsf/3efedde4322fef19862567740067f3cc/3a6899738157ea8986256ac5004bc0a7?OpenDocument
Mika Fukuchi
Application Engineer
National Instruments