"Requires installation of untrusted packages" problem in Ubuntu 10.10

I was trying to install a software from ubuntu software center, but several time it shows me "Requires installation of untrusted packages" The action would require the installation of packages from not authenticated sources.
I searched for a solution but get no good instruction to solve the problem.

Help me to get out of it.
Thanks in advance.

there can be more than one situations. For a temporary solution, you can try installing using terminal. It should repeat the same warning, but you will be asked to answer Y/N for installing after that.

for a better solution, you need to tell what are you trying to install.