Yes, actually, I do have some more ideas, but if they don't work, then I'll have to figure out something completely different.
First, even though this is probably 99.9% unrelated to the problem, make sure your graphic card driver is completely updated. -I'm sure it is since Windows updates most of its' software itself- and also make sure all of Windows Updates are installed.
Second, did you give the rscache directory enough permission for it to update itself? Set the permissions to full control if possible, by right clicking the file and under properties, clicking on security and modifying the current settings.
It should look like this...

Also, make sure that the file you created isn't interfering with any other Jagex related existing file. Like as you see mine is called, .jagex_cache_32 or something with "Runescape" or "Jagex". These folders should be located under your C: Drive. This is because if you have created another directory which also commands Runescape to write files to, then your computer will probably conflict to where to write the files to.
Example:

If the problem still persists, try playing in Un-Signed mode, which you can change the options to get into from here... (You must be in Internet Explorer for this to work.)
http://www.runescape.com/options.wsIf you still can't get in, then try CCleaning. I know it sounds pretty dumb, but there's a program called CCleaner which cleans out all your INDEX.DAT files. (Files where all your history and hidden cookies stay at, they are almost inaccessible and you probably never noticed them.) I always use CCleaner because it takes care of Temporary files even from Mozilla that just wont go away. -CCleaner isn't risky, but use at your own risk, because it might delete something that may be important. Don't use the Registry Cleaner because you have no use for it.-
Example:

Otherwise, did you try the Official RS Client yet?
If this didn't help at all, please tell me, I'll try to figure out something else. I would tell you how to re-script how your cache writes, but every computer is different, so it would almost be impossible for me to tell you exactly what codes to execute.
EDIT: Although this is completely unrelated, and probably wont fix anything, you could always try a System Restore. I know it doesn't have to do anything with the internet, but a file which might have gotten messed up could get re-solved that way. I wouldn't recommend it though.