Syntax errors Edit
JSON is a harsh mistress, as harsh as any other dominatrix you may know -- hey, we don't judge. A single error that appears anywhere in your syntax in your .xie file will render the whole file unusable by the game engine, and it will not successfully load your content. Even just a misplaced quote, comma, or brace will result in the entire file being rejected. What's worse, when the error occurs, it only indicates the point where the JSON parser got confused -- the actual error can occur on a different line entirely. Usually, if an error is indicated on a line, the problem that caused the error is actually on the line above the indicated line. For instance, if it tells you it encountered a quote when it was expecting a closing brace, that usually means you forgot a quote on the line above.
JSON validation Edit
The use of a JSON validator like JSONLint can really come in handy for persons new to the syntax, because it will give you a much more accurate indication of where the syntax failed.