The file structure on the CERC CompactFlash cards must be as follows

 File: xilinx.sys
 Folder: CERCxxx  ---->  File: xilinx.sys
                   \-->  Folder: rev0     --->  File: rev0.ace

where "xxx" can be the version number or some other string.

To write a new firmware version to a Compact Flash card:
 1) Download the new version as a zipped file from the web to a temporary area
 2) Unzip (in Windows, usually right-click on the zipped file) into the area.
 3) This may unzip to give the top-level file and folder as above or a single
    folder containing the two top-level file and folder; if the latter, then
    go down into this folder to see the top-level file and folder directly.
 4) Copy the top-level file (xilinx.sys) and folder (CERCxxx) directly to the
    CompactFlash card.
 5) Insert the CompactFlash card into the CERC (you do not need to power the
    board down first) and check if the clock LEDs restart.