ALL VISTA USERS
I have the ultimate solution to this problem:Error_loader_savefile - Unable to save to cache.
Runescape has downloaded a new update, but is unable to install it. It seems you do not have permission to write to the directory which RuneScape is using. To solve this please either:
Login as the user who originally installed RuneScape on this machine, and then try loading RuneScape again so it can update itself.
Login to your computer as an 'administrator' user, and then try loading RuneScape again. This should give it sufficient access to update itself.
If you are unable to do either of the above, then as a last resort you can tell RuneScape not to store any files on the harddisk. When entering the site and choosing between high-detail/low-detail also select 'Unsigned Applet Using Default Java' from the dropdown scroll at the bottom of the detail select page. You will need to do this every time you load the game. The disadvantage of this is the game will load slower and use more memory, so if possible use one of the top two solutions instead.
If problems persist then please refer to our technical-FAQ which can be found in the FAQ section of our website
Simply go to the "community" section of the runescape site and click "downloads and wallpaers", then download the windows client.
Once you have downloaded the client RSHD should work in that screen.
After that go to runescape in your browser and select "runescape HD" and you should NO LONGER get "Error_loader_savefile - Unable to save to cache."
P.S.- it work for me and i myself is a vista user and it should work for you too =)