WotLK Problem Arena Fights

Invisible character
Hi,

I've got recently some troubles with Wrath of the Lich King (arena). One of the two enemy becomes invisible (like literally) and it's impossible to have his position unless I click on gladius to get his "red circle" but he will stay invisible all game long. This happen only in arena (skirmish as rated). Understand that it's quite annoying when you try to play :s

I really don't know what it could be (especially that it happens only sometimes). It's not every game. :/ and i try old , and wod wow client. same...