Are you using a cloud drive such as google drive or onedrive by any chance?
Can you post a picture of the actual error message?

Hi, Thanks for responding. The database is on my PC; no cloud files, strictly local.

If the listbox is bound to a field on the form, then the listbox's entries must conform to that field's data type as set in the table.  For instance, if the field is a numeric field in the table, then the listbox can't have any text entries, or you get an error.

Hi, Thanks Kevin for responding.  The fields conform to their specific data types. I am receiving error notifications after trying to edit fields that were already established; the new value items are of the same type and I then get an error message when trying to close the edited field.  Any other possibilities? Thanks and I hope everyone is having a lovely season.

You need to Troubleshoot this issue. Rule out exactly what isn't causing the problem so you can deal with what is. I can see you've done some stuff already;

Have you tried running the database on a different computer?
If it works - The problem is outside the database, such as the office install, directory etc..
If it doesn't work on another computer, its definitely a problem with the database itself.

I'd also try repairing your office installation, just to be sure - https://support.microsoft.com/en-us/office/repair-an-office-application-7821d4b6-7c1d-4205-aa0e-a6b40c5bb88b

Have you tried copying just the elements you need into a clean database file and running it again?

Is the database running from a Trusted Location?

This should help us narrow down where the problem is

Hi Carrie, in the "Edit List" window, copy the listbox's entries and paste it to Notepad.  Delete all the listbox's entries.  When the listbox is empty, paste the entries from Notepad back into the listbox.  Try adding to the listbox again.  Also try adding entries in Notepad, then paste to the listbox.  All this is just to eliminate certain possibilities of what is causing this.  It could be a bug in Access, or a legitimate reason for this to occur.

Hi! I appreciate your suggestions, I tried all to no avail so I ended up recreating the database. Fortunately I was able to import the form unbounded and reconnected the fields, etc., and it works fine 'so far' : )   Next question from a user perspective as one who is entering data and then retrieving data.  When entering data, is there a way a person could select two options in a listbox and have those two choices be saved in the database? And, is there a way when forming a query to be able to search for two items within one field? For example when matching someone with available living situations. For instance in the first case, a person wishes to look for residence in two possible cities and so it would be desirable to enter two city names.  In the second case, a person wishes to search for all records containing either of the two city names. Sorry for the long post; I volunteered to create a database for an organization that matches seniors without homes with available homesharing opportunities. Being able to get help like this is awesome.  Thanks in advance!  : )

You can select multiple items in a listbox, but you cannot store their values.  If you turn on the "Multi Select" property on the listbox's property sheet, the listbox itself will have a Null value, because it can't store multiple values.

The only way to store multiple values in a single field is use a "multivalued field."  But you can only change its value list in table design.  You cannot edit the value list freely on a form like in a listbox.  Also, multivalued fields are cumbersome to work with, and are not recommended by many pros, including Richard himself and his moderators here.

The more common (and preferred) way to store multiple values is to store them in an additional "child" table, and create a one-to-many relationship between the parent and child tables.  Your form will need to add a "subform" to contain data from the child table.  This method lets you edit data freely and be able to save them into tables, hence the preferred method.  There are quite a few courses that cover "one-to-many relationships" and "subforms" since these are pretty big topics.