The following list shows both 'page' and 'image' hits for all status codes except 200 (Okay) and 304 (Not modified).
You can check the exact cause for error codes in the error logfiles on your webserver.
Status 404 (Not Found Requests) : 301 116 /robots.txt 34 /s2kreg.html 22 /global.html 14 /s2k.html 11 /opthreat.html 9 /opclass.html 7 /optrain.html 6 /opteam.html 5 /buckbio.html 5 /eastbio.html 5 /nsp.html 5 /opscen.html 5 /opterror.html 4 /erikbio.html 4 /marthbio.html 4 /opcomp.html 4 /russbio.html 3 /blackbio.html 3 /changbio.html 3 /favicon.ico 3 /glummbio.html 3 /marcbio.html 3 /oscarbio.html 3 /siddbio.html 3 /tedbio.html 2 /danbio.html 2 /hambio.html 2 /larrybio.html 2 /opserv.html 2 /opwater.html 2 /square.gif 2 /timbio.html 1 /chart.html 1 /exec.html 1 /trav98.html