Weird P2B P3 Katmai Problem

I have two systems with the following specs :

-Asus P2B-L, rev 1.02, bios 1012
-P2 300 klameth
-128mb of non-ecc 100mgz SDRAM (bought in Q3 1998)
-Maxtor 7200rpm 20gig
-Voodoo5 64mb agp
-Soundblaster Live Value
-External Nortel DSL Modem
-Generic 36x cdrom
-250w power supply

Both computers work well, no problems.

I recently purchased two P3 600mgz slot1 katmai's for the above systems.

Asus' site says the P3 600 works with my P2B-L:
http://www.asus.com/products/mothe [...] umper.html

-On one system, it works great.

-On the other system, it blue screen's and freezes all the time (behaving like a badly overcloakced cpu).

Question is why ?

The chip is good and a katmai 600, both chips work in one system, but none work in the other system. Both systems mobo's are the exact same revision purchased in Q3 1998.

I'm thinking the problem may be:

-bad motherboard, something wrong with its voltage, works with a P2 300 but not a P3 600.

Any thought or suggestions appreciated.

Cheers,
Marduk