you're right that your problem is most likely media.

memorex outsources to whomever is cheapest that hour. the same exact package could have any one of about 6 or 7 different manufacturer's discs inside.

solution: purchase quality discs (verbatim or taiyo yuden) and burn them at the RATED SPEED. your initial errors that caused you to reduce burn speed were probably also due to poor quality media. burning too slow is often just as bad as burning too quickly! do not use the "max setting" simply set for the rated speed of the media or SLIGHTLY lower. i would never go slower than half the rated speed. rated speed is ideal.

also, i'll assume that your firmware is up to date since I'm nto familiar with the liteon updates, but up to date firmware is always very important as well.

also, if you're wondering who actually makes your discs, use a program like nero cd-dvd speed (disc info tab) or dvd identifier. this will tell you what manufacturer made the media you're using.

Verbatim discs are almost always MCC media codes (mitsubishi Chemical COmpany) and Taiyo Yuden make their own media (TY or Yuden codes).

your memorex discs are HIGHLY unpredictable as to what manufacturer actually made them making them very undesirable to purchase because you nver know what is inside.