Current Perl documentation can be found at perldoc.perl.org.
Here is our local, out-dated (pre-5.6) version:
the perldiag manpage has a complete list of perl's error messages and warnings, with explanatory text. You can also use the splain program (distributed with perl) to explain the error messages:
perl program 2>diag.out splain [-v] [-p] diag.out
or change your program to explain the messages for you:
use diagnostics;
or
use diagnostics -verbose;