Dumping Physical mem to HardDisk

while working with windows professional 2000, sometimes my system show this message “dumping physical memory to harddisk” then its shows 1 -100percentage in blue screen, and the system get restarted, but there was no problem like this when i was using win 95 in the same system, is it bec of the minimum hardware requirements , i have pentium 550, 64mb ram,
is it bec of this or what can be the reason