Also in LabVIEW>> Find Examples>>Building User Interfaces>>General>> find the frollowing sample vi's
You can have your Sub VI's FP on the Tab Control of the Main VI.
All you ve to do is place a Sub Panel on each Tab page wherein you wish to call different Sub VIs.
See the attached VI in LV 7.1 for more details & modify it as per your requirement.
Do you keep growing any array uncontrolled inside your code ?
If you post your code or screenshot, it ll shed some light for us to fix it up.