I have written a main session that zooms to a sub session that prints packing lists. The sessions run fine but by the end of the day there are multiple copies of the sub session open. Why does this happen and how can I correct this? Thanks.

Hi,

This probably has to do with the mode you start the zoom session with. Use modal mode instead of modeless.
See library:

MODAL The parent session is blocked until the child session exits, in case of a multi-occurrence the session will be started as a zoom session.
MODELESS Parent and child are parallel sessions that can be manipulated simultaneously.