I would like some general advice on error handling please.

In my code once a user has filed out some values on a form the system
tests for a multiuser workbook being open. Only when it gets the book as read
write will it update the workbook then save it.

Could you give me some advice on where to go with the problem of errors
ocuring in the update. e.g. if the user leaves a the date textbox blank or
types text then a error 13 mismatch occurs and the program stops with the
multiuser workbook open.

I would like to avoid this for two reasons.
1. as its password protected i dont want the users in it.Just the form to
update it.
2. if it crashes and a user leaves it open then it will prevent other users
being able to update the data.

any advice on how to make sure everything completes between opening and
closeing the workbook would help.
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Regards and Thanks for any assistance.

Francis Brown.