Fabio, I've also had problems with multiple Timer events for one Timer queuing up. This has happened even if the first thing done in the Timer Event is:

This.Interval = 0
This.Enabled = .F.

The only way I could handle it was with a Form property lBusy:

If ThisForm.lBusy Then
   Return .F.
Endif
ThisForm.lBusy = .T.
This.Interval = 0
This.Enabled = .F.

*- ... other processing here

*- Restore Interval and Enable
This.Interval = 1000
This.Enabled = .T.
ThisForm.lBusy = .F.
Return .T.