Video display problem Snack/Radeon X300

Hi,
I have just installed ActiveTcl on a new computer and i have a problem
of display with the canvas used by snack (waveform and spectrogram) :
Even with the simplest demos (e.g. widget), the canvas are empty and not
updated when changing the signal, etc.
It looks like a video card problem, but even desactivating the hardware
acceleration does not solve it.
does it sound familiar to some of you ?

Thanx

Here is my config:

Win XP SP2
ActiveTcl8.4.11.2.201775
Snack 2.2.9 updated from the KTH website (same pb with the one of the
activetcl distribution)
Video card : ATI Radeon X300

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