If you have any other receiver on the same dish, which includes SKY boxes as well then they will hold the lnb in the Horizontal alignment and SBS is on Vertical. As above, turn them all off and check then.
Then, if no joy, you might want to check the lnb is aligned properly, rotation wise. SBS is a weaker signal and the lnb needs to be fairly spot on to receive it correctly.
Some of the Oval/10750 ex sky lnbs are failing at the moment, so the next question really becomes.... "What type of lnb have you got?"
Snap! I moved into this house with a Sky dish already installed with an oval LNB so didn't set up my own dish and LNB. I suppose the free lunch doesn't last forever so its a "heads up" to set my own up before the LNB fails completely. So much to do...