The first think you should do is get the error message from the error log file.

The problem is that you never import header. Replace
use CGI;
with
use CGI qw( :standard );

Also,
#!/usr/local/perl -w
should probably be
#!/usr/bin/perl -w

I'm surprised by your claim that it works from the prompt. It shouldn't, and it doesn't on my machine.

Unquoted string "header" may clash with future reserved word at 563851
+.pl line 4.
Name "main::header" used only once: possible typo at 563851.pl line 4.
print() on unopened filehandle header at 563851.pl line 4.
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