Bad... avast prevents sending necessary files to boot to Chest to avoid this problem.
You can't run Chest in Safe Mode, so you can't restore them.
Maybe you can copy the Chest contents to another computer (<avast>\Data\Chest folder) that has avast, restore the file to an USB drive and try to use the file (if it is not infected, i.e., if it was detected but it is really clean, it was a false positive).
Can you post the file name/path?