JSLint and JSHint will throw the "Unclosed comment" error when they encounter a multiline comment that does not end with the characters */. Here's an example:
/* MultiLineCommentCharsopt */
We can see from the above quote that multiline comments must end with the */ characters. If you have an unclosed multiline comment a syntax error will be thrown when the interpreter reaches the end of the file. Here's the above snippet once more, except we've closed the comment this time:
As you may have noticed if you have switched one of the example above to use JSHint instead of JSLint, a large number of the same error appear to get generated for the first unclosed comment, to the point where the parser gives up and tells you that there are too many errors. Fixed as of JSHint 1.0.0.
In JSHint 1.0.0 and above you have the ability to ignore any warning with a special option syntax. Since this message relates to a fatal syntax error you cannot disable it.