unable to upgrade to lenny

["raman narasimhan" <ramsn88@gmail.com>]

added deb http://ftp.de.debian.org/debian lenny main to apt and tried upgrade... got this error:

debian:~# apt-get -u dist-upgrade
Reading package lists... Error!
E: Dynamic MMap ran out of room
E: Error occurred while processing rosegarden (NewVersion1)
E: Problem with MergeList /var/lib/apt/lists/ftp.de.debian.org_debian_dists_lenny_main_binary-i386_Packages
E: The package lists or status file could not be parsed or opened.
debian:~#