A brief response to someone asking about a paranormal disturbance at the Real Magick & Occult forum. The person(s) had returned to a place in the woods where they used to practice magick, only to find that a 'force' or entity would watch them and prevent them from entering the main area to perform their rituals.
Some possible explanations based on the info you've provided so far:
1. If you didn't banish properly every time you've worked in that location then it's possible that the residual energies left behind could be attracting entities that like to draw off them.
2. Energy left behind and in-place (from not banishing and breaking down energy structures and dispersing residual energy after rituals etc.) might also have coalesced into thought-forms in your absence. These can seem like incomplete simple spirits that wreak havoc sometimes.
3. If you neglected to close portals (elemental) properly then it's possible that nasty things may have wandered in and out at will while you were gone.
4. The last possibility that pops in my mind is that your activities may have been disrupting local spirits and they weren't too happy to see you returning. However, ancestoral spirits that I've run into in native areas in the recent past have tended to be more active and immediate when someone does something they don't like. If you were allowed to practice in that area for a while before, then I doubt this is the case.
I'd look more into the possibilities of problems caused by improper banishing (#'s 1 - 3). That sounds like the most likely explanation to me based on what you've described.