If you perform a system restore from image software such as Ghost, the NPS-APACHE.CONF could become truncated in the process. (This file is located in SYS:\tomcat\4\conf.)
If the NPS-APACHE.CONF file is truncated to NPS-APACHE~1.CON or some other corrupt filename, use bash or another text editor to rename the file, then stop and restart Apache and Tomcat.