David putting the enabled property of the timer to .f. should disable the timer is anyhere in the code putting the timer enable again?
also the timer will fire in the interval that you specifie being this if your interval is 500 miliseconds and the code takes 2 seconds to run then the timer will fire again while is running the code.
you can also try the following in the timer event:

LOCAL lninterval
lninterval = This.Interval
This.Interval = 0
...run the code
This.Interval = lninterval

>How do I stop the timer firing while in a timer event?
>Lets say I have a timer, tim1, on a form.
>If the first line of the tim1.timer() event is
>this.enabled= .F.
>shouldn't that stop the timer firing again.
>Yet if I debug and step through the code, the timer keeps firing.
>If I put
>this.interval= 0
>in the first line the debugger stops and looses its place.
>I'm sure I used to be able to do this somehow??
>
>Also, if my timer() code takes 2 seconds to run and the interval is set to 500 milliseconds, the timer seems to re-fire whilst in the middle of the code execution. Should that be?