The apache2 server frequently stops with the error below. (When I manually (re)start the apache2 server, it starts okay.)

The error messages in the apache2 log:
[mpm_prefork:notice] [pid 19521] AH00171: Graceful restart requested, doing restart
[:notice] [pid 19521] mod_python: Creating 8 session mutexes based on 150 max processes and 0 max threads.
[:notice] [pid 19521] mod_python: using mutex_directory /tmp
Fatal Python error: PyEval_SaveThread: NULL tstate
[core:notice] [pid 19521] AH00060: seg fault or similar nasty error detected in the parent process

Does anyone know how I can fix this?

Thank you!