This is a recent problem for me. The raw files in question are ".pef" files from a Pentax k100d that I've had for quite some time.
I started having a problem with Bridge crashing on me. In trying to solve that problem, I started Bridge by holding down the crtl key and choosing the three option to reset preferences and purge cache. Since doing this, all my thumbnails have disappeared and I can't get them back. I've read and found the appropriate locations for the camera raw plugins:
I am running 64 bit Vista. I have CS4 and found that the latest version of Camera Raw that I could install was version 5.7. I found the install instructions on the Adobe site. As it told me to do, I downloaded the zip file for version 5.7 and extracted. I moved the Camera Raw.8bi file from the top directory into C:\Program Files (x86)\Common Files\Adobe\Plug-Ins\CS4\File Formats and moved the Camera Raw.8bi file from the Win64 folder into C:\Program Files\Common Files\Adobe\Plug-Ins\CS4\File Formats.
I also found the 5.7 Camera Raw installer and ran that. I am still having the same problem.
I have spent the better part of two days googling and trying to figure out what I am doing wrong.
I've tried moving all my cache files and letting them regenerate. I've purged the cache several times. Nothing I do works.
I do notice that when I go to a directory of photos that I have not been to in a while, I see the thumbnail for a brief moment. It quickly disappears and the flower icon appears.
Do I need to re-install Bridge? Do I have to uninstall first? I can't do that separate from Photoshop can I?
Any help would be greatly appreciated.