I am having an issue with a main form and subform. I enter the information on the main form and then the associated data in the subform. Everything is OK until I enter the Lot#, which is the linking field between the two forms, on the main form. When Lot# loses focus, the data in the subform disappears on the form. However, when you go to the subform table, the data is there but it doesn't have the linking lot# associated with it.
In the main form, change to "design view", then right click on your subform and bring up the "properties". You need to check to make sure the "Master Linking Fields" and "Child Linking Fields" properties are filled out with your linking field.