HELP! Ghost subjects are haunting me!

[JKeena]

I've been shooting with my Pocket Wizards and 550ex flash. When I get the slides back from the lab some are pretty good but on some my subjects (skateboards and bikers) are ghostly. This means the flash isn't strogn enough to capture them but my light meter was telling me to use that shutter speed (around 1 sec) when I plugged the aperture (are 4). I could only open the aperture another half a stop, 1 stop at most. Some of the pictures I am handholding but others I am using a very sturdy tripod. These particluar most recent bad pics are shot with a 15mm lens so I am really close (with in 8ft) and the flash is on the camera. Other pics I shot had the 550ex on the floor facing the subject. What should I do to get my subjects from disappearing? -Justin

P.S. This is THE most annoying monkey on my back for too long. I can get great skaters doing great tricks, timed perfectly and with good composition. I just get stuck with ghost skaters! Grrrrrrrrrrrrrrrr.

P.P.S. Actually, here is another thing. When I use my $25 Vivitar 283 it is lighting the subject even better than my 550ex! ( I put a Vivitar SL-2 optical slave on the Vivitar flash). I can see shadows on ceilings more than 25 ft high! And the Vivitar I'm just manually setting to the "yellow" setting and crossing my fingers with it being around 8 to 15 ft away from the subect. The 550ex I'm trying to control and so far crossing my fingers works better than anything else! ok, I'm done. Thanks!