Sounds like it is one of these problems:
alpha z-order problems, use additional or multiplying blending modes instead.
Graphics-Card Driver problem - try to get the latest update for you Cards drivers. (Seen disappearing alphaed meshes problems on Ati Cards)
alpha z-order problems, use additional or multiplying blending modes instead.
Graphics-Card Driver problem - try to get the latest update for you Cards drivers. (Seen disappearing alphaed meshes problems on Ati Cards)