When I try to compile your code at the command line, it complains very loudly:

c:> perl -Tc 889712.pl

Status: 500
Content-type: text/html

<h1>Software error:</h1>
<pre>Global symbol &quot;$name&quot; requires explicit package name at
+ 889712.pl line 11.
Global symbol &quot;$extension&quot; requires explicit package name at
+ 889712.pl line 11.
Global symbol &quot;%allowedext&quot; requires explicit package name a
+t 889712.pl line 15.
Global symbol &quot;$extension&quot; requires explicit package name at
+ 889712.pl line 15.
889712.pl had compilation errors.
</pre>
<p>
For help, please send mail to this site's webmaster, giving this error
+ message 
and the time and date of the error.

</p>

[Tue Feb 22 22:34:08 2011] 889712.pl: Global symbol "$name" requires e
+xplicit package name at 889712.pl line 11.
[Tue Feb 22 22:34:08 2011] 889712.pl: Global symbol "$extension" requi
+res explicit package name at 889712.pl line 11.
[Tue Feb 22 22:34:08 2011] 889712.pl: Global symbol "%allowedext" requ
+ires explicit package name at 889712.pl line 15.
[Tue Feb 22 22:34:08 2011] 889712.pl: Global symbol "$extension" requi
+res explicit package name at 889712.pl line 15.
[Tue Feb 22 22:34:08 2011] 889712.pl: 889712.pl had compilation errors
+.
[download]

You are using strict (as you should), but you need to declare and initialize all your variables ($name, $extension). You created an array variable (@allowedext), but then tried to access it as if it were a hash.

See also Troubleshooting Perl CGI scripts