add: if (err instanceof String) return err; 
context: function errorToString( err ){    if (err instanceof Error)        return err.message;    switch (err) {    case NS_ERROR_OFFLINE:        return "NS_ERROR_OFFLINE";        // xxx todo: there may be a more comprehensive API for these:    case Components.results.NS_ERROR_INVALID_ARG:        return "NS_ERROR_INVALID_ARG";    case Components.results.NS_ERROR_NO_INTERFACE:        return "NS_ERROR_NO_INTERFACE";    case Components.results.NS_ERROR_NOT_IMPLEMENTED:        return "NS_ERROR_NOT_IMPLEMENTED";    case Components.results.NS_ERROR_FAILURE:        return "NS_ERROR_FAILURE";    default: // probe for WCAP error:        try {            return wcapErrorToString(err);        }        catch (exc) {            return ("[" + err + "] Unknown error.");        }    }}
meta: 8395	/local1/tlutelli/issta_data/temp/all_js/javascript/2006_temp/2006/8395/c15df7d4539313b0292af0f9cc431bfe22d7f922/calWcapErrors.js/clean/calendar/providers/wcap/calWcapErrors.js