The CMC products that have CMC media codes are extremely variable in quality. This problem has been partially addressed by firmware T9.
Of course it is possible that you got a bad spindle, since it is very unlikely that any spindle of this is identical. However, CMC E01 is known for making beautiful scans of discs full of invalid files. It is necessary to copy-test (rip back to HD) all of the CMC E01 discs. Burning at 4x for this particular media is a good idea if you have trouble, but they still need to be copy-tested.
Unless you're trying to burn on a Pentium 1 or a 486, your system should be able to burn at 8x. It could have virus interference, virus scanner interference, CPU/memory wasted by add-on programs running at startup, or not enough memory.
With a more limited system, you need about 60 mb totally free RAM for use as a software buffer, and then you need to insist that your dvd writer software use more memory for your software buffer in user settings.
For 4x burning, try the inexpensive Ritek product for less data integrity surprises later. Burn the discs at the rated speed.
For 8x burning, try the inexpensive Prodisc or the slightly more expensive MCC (verbatim) products.
If you want a good CMC product, try the Philips media code instead of the CMC media coded product. The C08 is sometimes marketed under the BenQ brand.