get error instead of result when using expression in access

[Guest]

In my form under 'control source' i have input my datediff expression but it
is returning result #Name?, so am not to sure what I have got wrong where.
I am not an expert on Access and am only self taught through books and
websites so struggling to to figure out what doing wrong.

 

[Al Camp]

kiwi,
It would have been helpful had you included your expression in your post.
Name errors are caused by one of the elements in your expression being
either misspelled, or not exisiting on the form, or not included in the
query behind the form.
Since it's a DateDiff function, I would expect one of the date
elements...