Appears to be a bug in older versions of Cwd.

>c:\progs\perl588\bin\perl 590788.pl
Abs path is C:\Documents and Settings\ikegami\590788.pl

>c:\progs\perl580\bin\perl 590788.pl
Cannot chdir to 590788.pl: No such file or directory at 590788.pl line
+ 2
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Update: Apparently, it was fixed in Cwd version 2.18.

Cwd 2.18  Thu Jun 24 08:22:57 CDT 2004

 - Fixed a problem in which abs_path($arg) on some platforms could
   only be called on directories, and died when called on files.  This
   was a problem in the pure-perl implementation _perl_abs_path().

 - Fixed fast_abs_path($arg) in the same way as abs_path($arg) above.
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Update: According to Module::CoreList, Cwd with the bug fix (>= 2.18) has been included with all versions of Perl since (and including) Perl v5.8.5.