In prioritized order:

• Run EndNote as an administrator (for Windows Vista).
• Reset EndNote defaults (“Edit -> Preferences -> EndNote defaults”). This seems to work most of the time. Make sure to close Word first. After having reset EndNote, close it, and then try launching it from Word.
• The library may be corrupted. Try running “Tools -> Recover Library”.
• If all else fails, reinstall EndNote

There are other possible problems, especially when upgrading from older versions, but these actions usually work for me.

(For Norwegian readers: If you are using the Norwegian version of EndNote, the error messages will be ‘ugyldig klassestreng’ or ‘serverutføringen mislyktes’.)

“It is best for the author to be born away from literary centres, or to be excluded from their ruling set if he be born in them. It is best that he starts out with his thinking, not knowing how much has been thought and said about everything.

A certain amount of ignorance will insure his sincerity, will increase his boldness and shelter his genuineness, which is his hope of power.

Not ignorance of life, but life may be learned in any neighborhood;

—not ignorance of the greater laws which govern human affairs, but they may be learned without a library of historians and commentators, by imaginitive sense, by seeing better than by reading;

—not ignorance of the infinitudes of human circumstance, but knowledge of these may come to a man without the intervention of universities;

—not ignorance of one’s self and of one’s neighbor, but innocence of the sophistications of learning, its research without love, its knowledge without inspiration, its method without grace; freedom from its shame at trying to know many things as well as from its pride of trying to know but one thing; ignorance of that faith in small confounding facts which is contempt for large reassuring principles …”

(Woodrow Wilson, “How books become immortal”, 1891)