SET FILTER expression is evaluated every time the pointer in a table moves not at the time where it's issued. Try following

lcFilterExp = [tablefield = "] + this.value + ["]
SET FILTER TO &lcFilterExp

This way if this.value ="SOMEVALUE" than you'll get

SET FILTER TO tablefield = "SOMEVALUE"

>Hello all
>
>i'v the following problem,
>
>i want to filter my grid upon a selection in a combo box
>so i tried :
>
>in combobox's click event:
>set filter to tablefield = this.value
>
>also tried to put this in valid event
>
>but in both cases i get the errormessage:
>"THIS can only be called from a method"
>
>thx
>
>Christian