use Config::IniFiles;

use strict; #try to have this all the time
use warnings; #try to have this all the time

my $cfg = new Config::IniFiles( -file => uc "test.ini", -nocase => 1); #uc is not needed, but does not cause trouble either
my @FileExten = $cfg->Parameters("FileExten"); #change bareword to a string
foreach my $FileExten (@FileExten) #explicitly declare your variable, same with other places
{
     my $FileExt = uc $cfg->val("FileExten", $FileExten); #again, bareword
     print "FileExtension is $FileExt\n"; #you don't have a variable called $FileExtension, so I removed the $
}