When I try to open Synaptic Package Manager I get an error message.

E: Type 'wget' is not known on line 40 in sources list /etc/apt/sources.lst
E: The list of sources could not be read
Go to repository dialogue to correct the problem
E: _cache -> open() failed. please report.

I can't access the repositories dialogue from Synaptic Package Manager due to the error message!

help please, thanks

You can edit the file /etc/apt/sources.list with any text editor. For example - you can click on the icon to get you an virtual terminal, then in the terminal:

su -
(enter root password)
cd /etc/apt
pico sources.list (or nano, vi, emacs - whichever text editor you want to use)

Then fix up the sources.list file. If you don't know what all the entries mean:
man sources.list

Thanks for that,
I had added a line to the sources.list to add the medibuntu repositories and this included "wget -q http://packages.medibuntu.org/medibuntu-key"
Assuming that was the problem I deleted that line.
But the problem is now

E: Type 'quit' is not known on line 40 in sources list /etc/apt/sources.lst
E: The list of sources could not be read
Go to repository dialogue to correct the problem
E: _cache -> open() failed. please report.

I have tried going back to 2.6.17.11-386 and 2.6.15-386 and still have the same problem.
I don't know what to try to get a further clue.

Surprise! surprise!
What ever the problem was the latest batch of updates for Ubuntu 8.04 has fixed it.
Cheers