problem R/W session variable

Hi all,

I am new to the rms. I would like to write to and read from session variable.

dim a as string="123"

mySession.Variable(0,a)    'to write to variable

dim b as string = mySession.Variable(0)   'to read from variable

but somehow the write to variable can not work. And i search around google, I saw some example:

mySession.Variable(0)=a  'to write

when i tried to read, it return me NULL

Thanks in advance