Clutch drag

[jim47]

I was getting bad clutch drag after some sand riding, so removed I my clutch cover and took out the clutch plates. The 2nd and 7th steel plates were warped.

img16.imageshack.us/img16/3977/plate3.jpg

Why only these two warped?
Can I just replace these two or should I replace the lot?
Any tips to stop this form happening again?

 

[BSWIFT]

No more than an entire set of fibers and metals are, I would replace them all. As for why just those two warped, I would only guess that they were worn slightly more but just a guess.
Sand riding puts an enormous load on the bike. You may have other wear you haven't noticed yet, such as chain and sprockets.