How do I force Craft to regenerate assets transform? I had to add an image size in the assets transforms; all my pics were previously uploaded, but when I use getUrl('headIpad'), it makes urls like this:

http://host.com/cpresources/transforms/4/

Instead of this:

http://host.com/uploads/team-photo/_headIpad/fall-back.jpg

I tried to use generateTransformsBeforePageLoad in my config but Craft generates an error:


  Internal Server Error
  Image “fall-back.jpg” cannot be found.


Any ideas?
If you simply go into your craft_assettransformindex table and empty it, that should trigger brand new transformations for everything.