How do I fix a “E: impossible to read the sources list.” error?

Question

I've upgraded my system from Ubuntu 11.10 to 12.04 yesterday and it gave such serious problems that I had to format the partition and re-install the OS from scratch this morning.

Now, I fixed all the main problems, but still I needed to install the old Synaptic since I need some specific software I could not find in the Software Center.

After installing Synaptic from Terminal, I was not anymore able to use nor Software Center, nor Synaptic. They open and then close immediately without any message. The only thing Synaptic says is (sorry: I0m translating the message from Italian):

E: Line 59 in /etc/apt/sources.list is not correct (dist parse)
E: impossible to read the sources list.
Check the problem in the repository configuration.
E:_cache->open(), failed, please report.

What should I do? Thank you every body for your help!

Answer 1

OP posted:

After asking the question, I tried the following procedure and it worked, so maybe it can be useful for others: I had in the source.list file this error:

52 ## respective vendors as a service to Ubuntu users.
53 # deb http://archive.canonical.com/ubuntu precise partner
54 # deb-src http://archive.canonical.com/ubuntu precise partner

and

59 deb http://archive.canonical.com/precise partner
60 deb-src http://archive.canonical.com/precise partner

I changed them as follows:

52 ## respective vendors as a service to Ubuntu users.
53 deb http://archive.canonical.com/ubuntu precise partner
54 deb-src http://archive.canonical.com/ubuntu precise partner

...

59 # deb http://archive.canonical.com/precise partner
60 # deb-src http://archive.canonical.com/precise partner

And now everything works!