Are you getting this error message:
# ps
{dev_change_flags} {dev_change_flags_R__ver_dev_change_flags}
Warning: /boot/System.map-2.4.17-Newnat does not match kernel data.
{dev_change_flags} {dev_change_flags_R__ver_dev_change_flags}
Warning: /boot/System.map does not match kernel data.
{dev_change_flags} {dev_change_flags_R__ver_dev_change_flags}
Warning: /usr/src/linux/System.map does not match kernel data.
PID TTY TIME CMD
3039 pts/0 00:00:00 bash
4000 pts/0 00:00:00 ps
#
Does it also happen with top?
First make sure that you have copied your /usr/src/linux/System.map to /boot/System.map.
If that doesn't work, then delete your /usr/src/linux directory (save your .config file), extract a clean fresh copy, apply any patches you want, recompile and install.