The inability to use ‘/UNINSTALLALL’ and ‘/SILENT’ in tandem is mentioned in the documentation:
The supported commandline arguments are:
/SILENT – Hides the graphical user interface and suppresses all dialog messages and error reports.
/PURGE – Removes all JRE related registry keys, files and directories.
/CLEAN – Removes only JRE registry keys from previous version.
/UNINSTALLALL – Run the built-in uninstaller for all versions of JRE detected. Does not support the /SILENT argument at this time.
/UPDATEDEFS – Downloads a new copy of the JavaRa definitions, without a version comparison.
Use your network administration tools to perform the uninstall and then use the ‘/PURGE’ argument to do the rest.
Of course, we’ll certainly try to work around this restriction in the future.