TimerFcn doesn't stop

t = timer('Period',
 d,'TasksToExecute',4,'ExecutionMode','fi
xedSpacing');

t.TimerFcn = 'improcess'

start(t)

***********
the code above is working fine .... this code will call improcess
M-File for infinite and that's what i want.
it is working .. but the problem is that I can't stop it ... I tried
stop(t) and other command but nothing happens. it will stop if i
close Matlab program.

Ali