[SOLVED] $apt-get update problem

I was trying to install glest, a free RTS game from the debian repositories with:

$ sudo apt-get update

Reading package lists... Error!
W: GPG error: http://archive.canonical.com dapper-commercial Release: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 40976EAF437D05B5
W: GPG error: http://non-us.debian.org stable/non-US Release: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY F1D53D8C4F368D5D
E: Dynamic MMap ran out of room
E: Error occurred while processing tumiki-fighters (NewVersion1)
E: Problem with MergeList /var/lib/apt/lists/ftp.de.debian.org_debian_dists_sid_main_binary-i386_Packages
E: The package lists or status file could not be parsed or opened.

Don't ask me what they all mean. I just know that towards the end of executing apt-get update, I got them.

Anyway, luckily I stumbled upon an ubuntuforums post concerning almost the same problem and walla!

The solution was

$ sudo apt-get update -o APT::Cache-Limit=25165824