Does the PE1750 support 400Mhz processors?

I've installed a 400Mhz processor into my PE 1750 chassis after checking the support matrix here;

http://support.dell.com/support/topics/global.aspx/support/dsn/document?c=us&l=en&s=gen&docid=E424DB5EFA223486E0301E0A551743DC

...but I'm receiving a system error message during boot that a 400Mhz processor isn't suported and that it only supports a 533Mhz processor.

Do I need to reset the system to allow it to support the 400Mhz processors, upgrade the bios (currently at A06) or is the support matrix wrong and it only supports 533Mhz?

(accidentally duplicated my previous post - please delete if possible!)