This is usually a common problem associated with lighting.
If you are using the screen with natural daylight make sure there is no reflection from windows (the big holes in the wall filled with glass, not the one from mr gates
)
If you are using artificial light try not to use the centre light in the middle of the ceiling. Try to use uplighters that will direct the light away from the area you are working.
Trust me. In my day job I am a lighting engineer
