Check the log for TWIKI.
Wed Mar 18 11:52:53 2009] [error] [client 193.252.28.244] suexec policy violation: see suexec log for more details
[Wed Mar 18 11:52:53 2009] [error] [client 193.252.28.244] Premature end of script headers: configure
[Wed Mar 18 11:52:56 2009] [error] [client 193.252.28.244] File does not exist: /home/insightteam/public_html/favicon.ico
[Wed Mar 18 11:53:00 2009] [error] [client 193.252.28.244] suexec policy violation: see suexec log for more details
[Wed Mar 18 11:53:00 2009] [error] [client 193.252.28.244] Premature end of script headers: configure
[Wed Mar 18 11:53:10 2009] [error] [client 193.252.28.244] suexec policy violation: see suexec log for more details
[Wed Mar 18 11:53:10 2009] [error] [client 193.252.28.244] Premature end of script headers: configure
[Wed Mar 18 11:53:45 2009] [error] [client 193.252.28.244] suexec policy violation: see suexec log for more details
[Wed Mar 18 11:53:45 2009] [error] [client 193.252.28.244] Premature end of script headers: view
[Wed Mar 18 11:56:21 2009] [error] [client 193.252.28.244] suexec policy violation: see suexec log for more details
[Wed Mar 18 11:56:21 2009] [error] [client 193.252.28.244] Premature end of script headers: view
[Wed Mar 18 11:57:27 2009] [error] [client 193.252.28.244] File does not exist: /home/insightteam/public_html/favicon.ico
[Wed Mar 18 12:01:11 2009] [error] [client 193.252.28.244] script not found or unable to stat: /home/insightteam/cgi-bin/twiki