I also presently have this problem, it disappeared after I had reinstalled Premiere CS4 ( I am with Windows 7 32 bits) but it reappeared a few days after although I had not changed anything in my cam settings. Adobe says among other thinks the problem might be related to the PluginCache file and explains how to re-create this file:
“Some problems may be caused by a damaged PluginCache file. To re-create this file, hold down the Shift key while choosing Start > Programs > Adobe Premiere Pro. Release the key when the Select Initial Workspace window appears.”
In my case the procedure didn’t work; I don’t know which Windows 7 file is equivalent to the PluginCache file in Windows XP but I certainly have a problem with this file since Windows also stores the application preferences in it and I can see that some preferences that I correctly change are not saved when I re-open the project.