Web Player Activex in .net winforms not showing

Hello,
We’ve implemented a unity game embedded with web player activex inside a winforms application. It worked okay on xp 32 bit machines. When we installed on windows 7 32 bit(on the same machine that was ok with xp) we have a strange behavior. The game is loaded but we do not see anything. The game responds to clicks (we can hear the game sounds) but we only see a blank form. When the form loses focus we can see the game but it disappears again when the form becomes active again.
This also worked ok in one machine with win 7 64 ,but did not work with another win7 64 bit…
What can be the cause? is it related to OS or graphics?

We finally resolved this issue by disabling Aero theme for windows 7. Once we diabled it the problem was solved.