Darkness when leaving the body

Welcome to the forum pedroalmeida :)
Yes, I don't think its because of frontal chakra. Next time when you find darkness everywhere and you feel that you can't open your eyes, just say this a little louder "I need some light to see" or something similar. So this will open up your eyes when you are out and feeling dark everywhere :)
Its just your thought which sets you in dark place, just think that you can see :)

Your condition is by no means exceptional - Austrian occultist Alfred Ballabene described similar experience when using his technique of astral projection. Speaking for myself, when I used to travel far and wide (that was about ten years ago, unfortunately!) I would more than often "leave" the body to find myself floating in a limitless and featureless space, without sights or sounds - and without any awareness of my body, physical or otherwise. My take on it (heavily inspired by the Aurum Solis material) is that, once we dismiss the scientific reductionism with its notion that it is all in our heads, it is not the entire psychic (etheric, subtle etc.) substance that is projected but merely a part of it (otherwise we'd drop dead while projecting). This substance has intrinsic ability to register sensations such as sound, sight, touch etc. If the astrosome (astral or subtle body in tha Aurum Solis parlance) is weakened, it doesn't have the surplus of etheric substance to project outwards, which diminishes the quality of the projection experience.
In my opinion the condition should abate with subsequent projections. I once projected using the AO method almost by the book, but my astrosome was weak - I registered visual sensations, but they were blurry (similar to your experience). I've described the technique and the experience in the technique section.
One question - did you spell the mantra "FARAON" out loud, or just repeated it internally?

Edit: the length of conscious projection should increase while the astrosome gets stronger (and has bigger surplus of etheric substance to project). This means that the experience should get better with either more projections (where the etheric body might absorb more of the substance it is built of) and, definitely, with "energy absorption" exercises (I'd recommend either Golden Dawn "Middle Pillar" exercise, which used to help me in the past, or the Aurum Solis "Clavis Rei Primae").

Say the mantra "Clarity now!" or "I want to see!" Keep repeating it till the vision comes to you. If it comes blurry. Keep repeating it or say "I need to see clearly!" You need to focus energy to see, by repeating mantras you focus this energy. This was what was meant by energizing the frontal chakra.