The filename (_filename) in cachescheme HTMLVersionTable needs to be fixed.
The built _filename (path and filename) contains duplicate directory names. The
PluginCacheTable.cacheHome variable already has userHome and javaplugin.version in it. So you end up with a path like the below being created.

/home/user/home/user/java_plugin_AppletStore/null/null/html/version.table

From HTMLVersionTable.java

_filename = userHome
+ File.separator + PluginCacheTable.cacheHome
+ File.separator + System.getProperty("javaplugin.version")
+ File.separator + "html"
+ File.separator + "version.table";

From PluginCacheTable.java

cacheHome = userHome + File.separator + "java_plugin_AppletStore" +
File.separator + System.getProperty("javaplugin.version");