Just wanted to update... Turns out the problem was with my grow tent. I purchased one of those cheap, white-lined grow tents from eBay and couple of months ago and have had nothing but problems. Turns out the PVC on the inside of the grow tent was treated with a chemical to help make it flexible. That chemical happens to outgas when exposed to HID light and heat. There is lots of info about these poison tents out there, but many people are still unaware.
The problem surfaces as nute lockout, similar to a pH problem (take a look at my pics at the start of the thread)... Just an FYI..