What do you mean flashing issue? I don't understand what you are trying to get at with this.
Second Life requires a fair amount of VRAM for its graphic performance. If you have a card with limited VRAM, your best bet would be to upgrade the card. Otherwise it may be a cache issue. Look around in the settings to see if there is an option to clear the cache. Also, reduce the graphics settings of the application and see if that resolves it.
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