Errore APT: Reading Package Lists... Error!

[alberto <albertobig@libero.it>]

Ciao, 

Sto provano a tenere una distribuzione mista stable/testing

Ho messo questa linea lnel sorsces.list: 
 deb http://http.us.debian.org/debian testing main contrib non-free

Ho dato: apt-get update
Questo e' l'errore: 

Reading Package Lists... Error!                    
E: Dynamic MMap ran out of room
E: Dynamic MMap ran out of room
E: Error occured while processing xt-toolbus-doc (NewVersion1)
E: Problem with MergeList 
/var/lib/apt/lists/http.us.debian.org_debian_dists_testing_main_binary-i386_Packages
E: The package lists or status file could not be parsed or opened.


Qual e' il problema? 
grazie. 
-- 

alberto.