Warning: Cannot modify header information - headers already
sent by (output started at
/xxxx/xxxx/xxxx/xxxx/actions.php on line 120
This error basically means that who ever edited the language file (in this example above is the German language file) last didn't save it
correctly. It needs to be saved as UTF8 NO BOM (no byte object marks). So to correct the issue you will need to re-edit the language file (in this example German lang.public.php) and save it as UTF8 NO BOM and then re-upload it to your store replacing the bad one.