[iBook] iBook G4 stall after wake from sleep

[Tom Meade]

Hi - any thoughts about a pattern of stalls following sleep?
Even with all apps closed, airport "off" half the time the
cursor will freeze right away or is frozen at wakeup.
The longer the sleep (hours) the more likely the stall.
I'm suspecting temperature change in the microprocessor
or logic board because the incident seems less frequent
when the temp remains constant - as when the 'book
warm from use is kept on the power adapter for an
hour. But after several hours, when charging has
tapered off and the unit cools, there's a freeze.
My iMac, running 10.3.4 can sleep for days, but
temp remains constant as it's not on battery.
Final note - sometimes the iBook's screen will display
this message upon crashing:
System Failure: cpu=0; code 00B99EBO (B'S may be 9's)
(Unknown code) Latest crash info for cpu 0:
Exception state (sv=0x25649000).
Does the "256" indicate something abut RAM?
Tom