technical screen issue with MAcradiant 15

[fleash eater]

hello tremulous community,
     Im a usual mapper,and i have mapped for a few other games with my mac radiant , but this issue recently put me out of my mapping. whenever a rght click the 3D screen, i cant move the camera and i auto pans to the left..... does anyone know how to fix this?

[fleash eater]

soooo...any suggestions?