[kang]

If I recall correctly, the factory service manual specifically states NOT to use anti-seize on the spark plugs. The factory recommended plugs have a coating on the threads that prevents galling, just like the anti-seize would.

Perhaps the anti-seize you used, even if not near the firing gap of the plug, is preventing the plugs from getting a good ground via the heads. You might consider removing the plugs, cleaning the anti-seize off as best you can (hard to get into the heads to clean in there) and see if that makes your codes go away.

I don’t think dielectric grease on the electrical contact part, e.g. the plug wire, would cause any problems.