Ubuntu :: Cannot Do Non Critical Updates

I'm running 32 bit 10.10 on a Lenovo N200 laptop, I have 3 other Ubuntu computers on my home network and they don't suffer from this problem, 1 is 10.10 32 bit, 1 is 10.10 64 bit and one is 10.04 32 bit. they are on the same network and I cannot see a difference.

However when update manager says there are some updates available, I can install the critical ones but not the "other updates", it tells me that they would require installation from non authenticated sources then after agreeing will not install and goes back to the start of the update process.

The error message lists ALL the "other updates" if I deselect them then the critical upgrades down load and install OK.