Form Entry Not Valid

[tpearo]

I have a form that I use to allow tecnichians in my lab keep track of time they work on a project. Each technician has an Employee #. My form has a subform based on a query that when they type in thier Employee # their name appears on the form. Then the other two fields are Date and Time that are automatically set based on the system clock. Sometimes they will type in the wrong employee number and close the form. Is there anyway to set the field so that if they type in the wrong Employee # (another words a number that isn't in the employee table) that they get a message that says something like invalid entry... or does not let them close the form. I'm trying to prevent a mess of unnecessary data being put in the project table.

 

[spizotfl]

would changing the textbox to a combobox with all employee ids work better? then they would just select from a drop down list.