Proably some kind of bug or virus. You must be using windoze. Try unplugging you machine for a few minutes and then re-boot. If the problem persists contact micro soft. Make sure you have the latest...
Lexical refers to the "lexicon" or the kinds of words specific to a certain specialty or field. Think of it as slang or jargon, if you have a lexical inconsistency, the term you use in one specialty...