Macro to check for existing records

[GingGangGoo]

Is it possible to have an autocomplete textbox run a macro when no matching record is found, rather than just giving me "not matching records" message, stops, opens a specific popup and allows me to add a record.
I am using the autocomplete on a popup form to add participants to activities, but in my situation we will be adding participants from sign up/sign in sheets, where some folks have already been added, and some are new.

 

[bob fitz]

See: http://www.databasedev.co.uk/not_in_list.html

 

[GingGangGoo]

See: http://www.databasedev.co.uk/not_in_list.html[/QUOTE

I can't use vba in a web app, and there is no limit to list function to work with.