Made some minor changes, your code works. See comments for details.

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 s
+tring
foreach my $FileExten (@FileExten) #explicitly declare your variable, 
+same with other places
{
     my $FileExt = uc $cfg->val("FileExten", $FileExten); #again, bare
+word
     print "FileExtension is $FileExt\n"; #you don't have a variable c
+alled $FileExtension, so I removed the $
}
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