Memorex Dl are pretty crap really. I used them a while ago and out of a box of 25 not a single 1 burned without errors.
When burning make sure you burn the discs on the lowest possible speed. higher speeds can cause errors on a lot of DL media.
i use Verbatim made in singapore and even burning on the highest speed i get perfect burns every time. Verbatim made in india are lower quality though and you do get the odd bad burn even on low speeds