"Jamma" Nokia 5130 XpressMusic - Clock alert tones/Ringtones | Phone/Device Issues and Features | Consumer forum

I downloaded some other Nokia alerts and ringtones and uploaded on the internal SD card. For some reason-not known, when I'm trying to change the clock alert, with a new one, almost the whole list of alerts is "grey" and cannot be accesed and the message on the screen is: file is to large...
Same thing with the ringtones, only the message will be: cannot import from this Folder (or something close to it), even though I tried to move them in a different folder, same bad result.
Any idea, how to get around this and make those files work?(some of them are 25kB instead of 1kB...); Did I messed-up the original list of alerts? I did not do a back-up of the phone before trying all this stuff, unfortunately.
Any help/hint of enlarging the clock alert/ringtone list is much appreciated.

Thanks!