update-manager Problem

[das দাশ]

Hello Friends

I installed Ubuntu 7.04 on my laptop with a the live-dvd, and then I
added extra repositories exactly the way the Ubuntu guide suggests. And
then ran apt-get update and when I did run apt-get dist-upgrade, there
came an error message, the same message repeated with synaptic and
update-manager, the last one suggesting me to report this. I am quoting
here the whole message verbatim:

<<<
_Could not Initialize the package information_

A unresolvable problem ocurred while initializing the package
information.

Please report this bug against the 'update-manager' package and include
the following error message:

'E:Dynamic MMap ran out of room, E:Error occurred while processing
nvidia-glx-legacy (NewVersion1), E:Problem with
MergeList /var/lib/apt/lists/
security.ubuntu.com_ubuntu_dists_feisty-
security_multiverse_binary-i386_Packages, E:The package lists or status
file could not be parsed or opened.'
>>>

I don't know, if this is relevant, the VGA and audio are all SiS,
nothing to do with nvidia. 

What can I do now? This is a peculiar situation: I cannot update
anything. The orange star of the update manager, when I click, is giving
the same error message. 

---
das