Strange Flash Transmitter problem

Hi, I have on of theseand it works fine on my 5Dmk2,

A frend tried it though on his 550D and we are tottaly unable to get it firing. His 550D works fine with a 430exii, so Im at a total loss as to what the problem might be.

Any suggestions would be appreciated!

What flash are you trying to trigger?
Does the "test" button work?

sorry, got it working...

Needed new batterys, which is odd, as it works fine on my 5D, but for whatever reason only works on the 550d with new batters.