Camera Raw files from Leica (.RWL) and Panasonic (.RW2) files do not open in Photoshop CS4, and Bridge CS4 does not display their thumbails.
You ran the Camera Raw patcher to update from Camera Raw 5.0 or 5.1 to 5.2.
This is a known issue that occurs when you run the patcher instead of manually updating to Camera Raw 5.2.
See directions to install the update on on the Camera Raw download page at http://www.adobe.com/support/downloads/detail.jsp?ftpID=4219.
After you manually install the Camera Raw 5.2 update, the patcher will successfully install future versions of the Camera Raw update.