No reason other than a) Intel says I could use 400Mhz (PC3200) and b) it's faster that's all.

I wouldn't have even tried it if my manufacturers support team said I couldn't use it...but they said I could

I don't know, you can't rely on anyone these days!

Still, as I said, the Intel site says I 'can' use it...so I'm still confused why it's not working!

Dave