In VFP7 you'll get such error if cursor you're trying to alter has fields with names longer than 10 characters.

>I tested the next couple of functions at the command windows:
>
>create cursor cur_Temporal (campo1 c(10))
>alter table table cur_Temporal add column campo2 n(8,4)
>
>There were no problems at all.
>
>However, if try the same at the click event of a command button of a form, I get the error 1115 “Not a valid operation for a cursor object” (translated)
>
>Could somebody tell me what makes the difference?
>
>Thanks in advance
>
>Oscar Corte