Failed to fetch, cached failure, POSIX enz.

[L33dvermaak]

I jailbroked my iPod touch but I have some problems with Cydia

When I start Cydia this is what I get:
-First: "Downloading Packages.."
-Pop-up: "Error: refreshing Data"
(Including GPG error, Failed to fetch, cached failure, POSIX: operation timed out)
When I try to download a program form Cydia i.e. BossPrefs I get this:
-First: "Install>confirm"
-"Running screen"
-Pop-up: "htttp://apt.thebigboos.org
POSIX: Operation timed out"
-Anohter pop-up: "POSIX: Operation timed out"

I only have Winterboard sucessfully installed with the Telesphoreo Tangelo source (apt.saurik.com)

On internet there are rumours of different solutions
-Use an other wifi network
-Hardreset
-Delete sourcesc with OpenSSH
But what is the real fix?

Another wierd thing is that my friend did the same thing wit his iPod
And he dont get any errors...

Please help me. Thnx