Just a bit of a follow up on the advice I received here.

I stopped multi-tasking and continued to use the same media. Media that is being used is the Memorex. I could not dump these as I had another 100 left. I have been using a internal Sony DVD burner with speeds going up to 8x.

This had provided no problems for me and I am able to open the disc right after backing up..

I will have to try and use one of the externals that I had problems with and see if these are good back ups as well.

Thanks for the advice