how do you manually run synatic package manager

open a terminal (Applications->Accessories->Terminal) and type
gksudo synaptic
If this gives an error, please post the exact text of the error.

I forgot: you have to hit enter after typing a command into the terminal. It will ask for /your/ password in a dialog box.

Hi,

To run manually synaptic, open a terminal (Accessories / Terminal).

$ sudo synaptic
[sudo] password for your_user:

(When you tapes your password root, it's normal to not see any characters)

But I think that the «Error» is not synaptic. If the error persists, try running the command

sudo aptitude update

Maybe you'll see a message more understandable

Or to bypass synaptic altogether and get all the latest updates type

sudo apt-get update
sudo apt-get upgrade

E: dpkg was interrupted, you must manually run 'dpkg --configure -a' to correct the problem.
E: _cache->open() failed, please report.

There was obviously some failure with an install somewhere along the line.

The commandline that your error has reported (as Jim has pointed out above) will cause that install to be re-run and, hopefully, rectified.
I recommend that you subsequently do the two lines I indicated above since it will get the latest updates for all your installed packages.

You should then be able to run Synaptic through the System, Administration menu.

Thanks Jim Hutchinson, that solved my question.