I don't know when this appears and what is this:
then when I click on that icon its showing this:
When i clicking in
Show Updatesits bringing window
Update Manager, and there is no new updates.
Can anyone say what is this?
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Go to Software Center, click on the Edit Menu, and then Software Sources. Makes sure you have the "Main Server" selected as your "Download from:" location.
Then open a terminal and run
sudo apt-get update
sudo apt-get upgrade
That should get rid of the error. If you still experience it you may have added PPAs that are no longer available. In that case select the "Other Software" tab in the Software Sources dialog, and uncheck all of them. You can then recheck them one by one and see if
sudo apt-get update causes any errors.
Have you tried checking for updates manually from the command line and see if you're getting any errors?
I experienced this issue shortly after upgrading to 12.04, due to some PPA that hasn't been updated for precise. While all the other repositories were updated correctly, the update manager would still throw this error because of that single PPA that couldn't update.
I don't think I ever used the word update so many times in a paragraph