Could not set the RowSource property. Invalid Property Value error when switching bet

Hi,
I am using VBA to store and get the data from Access database using Userforms.
I used drop down and sub dropdown comboboxes for selection of items. 'Select case' option is used for better control of the comboboxs.
The Rowsource data for both comboboxes are from 'name manager' defined in the same excel workbook.
Combobox style is set to dropdowncombo.

The problem is, when I switch between excel workbook and come back to main workbook where userform is running, I get the error while clicking on the listbox line item to select and edit.
The application closes and again we have to start the macro. This happens only when we switch between workbook and come back.
If we continue work with same workbook it works fine.
Please somebody help to get rid of this.

Link to other forum: Link

work your way through the code in the attached file.
do not use 'rowsource' it is the most unstable method of populating combo/listboxes.
forget using 'name manager' - use tables they self maintain and their size is dynamically updated in 'name manager'
leave userform controls (textboxes/combo/listboxes) at their default names - you can then loop through them to load.

in userform properties set 'Show Modal' to false, you can access anything in the background, take care that the app sheets are in view when you start reusing the form.
You should copy in any data required prior to using the form unless you have written a process to import your data dynamically.