There are generally two parties to an easement. One is the servient tenant who owns the property; the other is the dominant tenant, who has the right to use the property for some specific purpose.
An appurtenant easement exists regardless of who owns the property and the rights transfer to new owners of the dominant rights. An easement in gross may expire when a dominant tenant moves or dies.
The wording of an easement usually prevails, but if the terms are not spelled out or are ambiguous, then a court may be asked to decide the rights and responsibilities of the parties.
A servient tenant may not block the rights held by the dominant tenant, and the dominant tenant may do things to the easement in order to ensure his rights may be exercised.
A third party, with no rights to the easement right-of-way, may not block the dominant tenant, and could be sued by him if they did.
You really didn't give a detailed description of your particular problem, or what your position is, so it's difficult to answer with anything but generalities.