Help with scratch disk/temp files

On my system I have small(330Mb) virtual RAM-disk R: . My system configured so that all temp-files, cookies, cache... all placed on this disk R: . Now - I try to work with Photoshop CS. I know, that 330Mb isn't enough for work files for Photoshop, so I try to tell it: "Use real hard-drive C: for you scratch file(s)". For that I went to "Preferences->Plug Ins & Scratch Disks" and set _ALL FOUR_ scratch disks to "C:\". All the same - when I start my work Photoshop CS create it's temp file(name like "Photoshop Temp4122672") exactly on R:, not on C:! Of course after 10min. of work I have stable error:
And so - how to force PS to use C: as storehouse for temp-files?

Thanks In Advance...

try holding Ctrl+Shift+Alt+W while PS starts up, you'll be prompted to trash your prefs file

[QUOTE=Lion of Judah]try holding Ctrl+Shift+Alt+W while PS starts up, you'll be prompted to trash your prefs file[/QUOTE]

Yes, I try this key-combo and I receive prompt. After I answer "Yes", nothing changes. :( Temp files still created on R:. I setup all scratch disks to C: again and reload PS - all the same. I think PS use environment variable TEMP(may be TMP) and both in my case point to R:\Temp\. Exactly in this folder PS create it's temp file. But I wonder - what option "Scratch Disks" do at all? It doesn't influence on something!