don't load language on local apache

[eluser]Unknown[/eluser]
hi guys,i've a small problem with a server apache on my ubuntu.
when i try to open a language file with "$this->lang->load('file')", page respond me with a funnier "Unable to load the requested language file: language/file_lang.php"..but if i copy all on a web server like aruba it works..i'm using CI with matchbox RC2(i try other version also)

on my ubuntu all work fine,DB is ok,mode_rewrite is ok..ONLY the language doesn't work

thx all