Reading the Help, it looks like your parameter is incorrect.

Help says the parameter is to be the VALUE to be assigned.



>>Might you have the variable "NULL" set to an empty string somewhere?
>>
>>good luck
>>
>IF .lAddblank
> =MESSAGEBOX(.name + " null? " + TRANSFORM(ISNULL(this.aRowSource[1,2])))
> endif
>
>Shows .t. Why would it change to blank?