#error using functions

[SM]

I am trying to use an expression in a control box but keep
getting #error. It doesnt matter what function I use, I
still get error. I have expressions in other text boxes
that work fine, what is wrong with this :
Heres an example of one of the expressions that doesnt
work : This is the exact text in the control source.
=Right([Cal_NameDes],4)
(I also tried using Right$, Trim, InStr...)

Cal_NameDes is a field from a table (Text, length 16), it
displays fine if I take the expression out and just put
[Cal_NameDes] as the control source.

Any Help appreciated.
Thanks!

 

[Liz McCracken]

What kind of control box? Is it a text box, combo box,
list box?