Hmpf, could be related to many things
AFAIK some problems with the RAM...

EDIT: NULL-Pointers, bad memory allocation/rellocation for the the process, getting memory space without rights to write to it... and and and... bäh, the www is full of segfault error-messages

EDIT2: Did you have swap enabled? How's your memory "consumption" Normally the system handles that stuff automatically, perhaps something went wrong. Did you restart your N800?