Hey I have had same problem not long after buying new tv. I have been on LG case for a while, their standard answer was never had that problem, but eventually after all of updates and resets they said to take it to local repair shop and technical department is recommended to replace motherboard. That has been done about 10 months ago and touch wood I haven't had out of memory fault. So my advice is if under warranty just keep in touch with LG and don't give up. I'm located in New Zealand and I have communicated with them via their nz Facebook account. Hope this helps.
