The error probably was introduced above the point where the message occurs. Sometimes an error occurs that allows LaTeX to continue with an incorrect interpretation of what is going on -- the content it sees is wrong, but looks like valid syntax -- until eventually a point is reached where the syntax is no longer plausible. Think of omitting a closing parenthesis in a programming language: depending on the language, the compiler may be able to continue parsing the code for a while before it becomes clear that the parentheses are unbalanced.
You may not be able to extract any useful information from the error message other than that there is a problem in the document somewhere above it. The message is not totally extraneous, though; there _is_ an error somewhere in the document. /Paul
