sudo su
cd /var/lib/apt/
cp -rf lists backup_lists #backup just in case

rm -rf /var/lib/apt/lists/* # clear this folder
mkdir lists/partial #restore the folder
apt-get update

This method helped some ppl on pc debian, but since maemo is debian based it should work also. If not then just restore the backup.

cp -rf backup_lists lists

I just realized something. Did you install easyroot before this happened? You need it to to get root access from terminal.