We are using ROCKS 4.2.1 (x86_64). I shot a worknode recently, however the installation stopped right after the "Reading Package Information" stage and prompted "Unable to read head list. This may be due to a missing file or bad media. Press <return> to try again." I checked the httpd logs of frontend, the worknode did download hdlist* successfully without error. But why it still complains unable to read head list? How should I diagnose and locate the source of the problem?