Welcome to the forum
LG drives are pretty picky about media quality, and the quality of Memorex discs can vary depending on who made them.
Can you download and run CD-DVD Speed, put one of the discs into your drive, and go to the “Disc Info” tab.
There you will find the Manufacturer and MID info for the Memorex discs - can you please post it for us?
Also. What model is your LG drive, and what speed were you trying to burn the discs at?