I've partially solved the problem...
In fact, by using:
rm -rf /tmp/orbit.$username
i succeeded in making evolution work correctly again.
The trouble occurs when i try to launch it using a script (i configured extra keys on my keyboard to launch evolution) but i'm not at all an expert in bash script, and something goes wrong each time i try.
Actually, i launch it from a eterm, and everything's work withou any problem. If someone know how to launch it by script without messing the whole thing, please let me know!!
Anyway, thanks very much for your answer!