Premature end of script headers

Hello. I watched logs and found some errors:

[Thu Jul 31 01:55:10 2008] [error] [client 65.55.211.121] Premature end 
of script headers: ref.cpdf.php
[Thu Jul 31 01:55:10 2008] [error] [client 65.55.211.121] File does not 
exist: /home/phpmirror/domains/php.frnet.ws/public_html/500.shtml
[Thu Jul 31 01:55:10 2008] [error] [client 65.55.211.121] SoftException 
in Application.cpp:245: File 
"/home/phpmirror/domains/php.frnet.ws/public_html/manual/zh/ref.zlib.php" 
is writeable by group

I've checked pages and I see correct pages.
Is it important to check this error logs?