if Greg is right about the timer vs webTimer, and it certainly sounds to me like that is likely the case not withstanding the Xojo version or if it’s a web project or not, I can say for sure that you need to get the proper session context setup for the control.
I just put something like this somewhere before accessing the controls properties:
Dim Context As New WebSessionContext( app.SessionForControl( Me))
assuming that Me is the control you’re talking to, otherwise put the control reference there.
This is somewhat voodoo in my mind as you don’t have to actually do anything with the context object once you fetch it, the act of having one in scope is enough to make it work. There are examples of that in the web documentation as well I believe.
Or... perhaps you are talking about something totally different ;) In which case the above will not be helpful at all ;)