40d Third Party Flash?

I have a 40d and a Promaster 7500dx flash. The 1st/2nd curtain sync is greyed out. Is there any way to get 2nd curtain sync with the 40d/Promaster? Or do I have to have one of the Canon flashes?

I don't know about that but I have a Rebel xt and xti and 2 promaster 7500dx flashes and they are the pits. Right in the middle of shooting (programmed or manual) they just quit for no reason..the pilot light is on but the info is not passed to the camera and vice versa thus everything is underexposed and the flash doesn't fire. I have to take the flash off the camera or bracket (after turning everything off), put it back on, turn everything back on and then the promaster flash will work again for maybe 5 or 10 more flashes, never more than 10 before screwing up again...Promaster of course is like Canon and denies there is a problem so good luck in solving any of your promaster 7500dx problems. I think I will go to metz next time. I have a 580ex II but too expensive to buy another one..anyway, good luck.

Nope not AFAIK. 2nd curtain flash is useless in 99.9% of cases, so forget about it unless you know you're in the 0.1%.