An UncategorizedApiException is thrown when a user hits their hourly rate limit. An authorised user is only permitted 350 API requests each hour, if this is exceeded an UncategorizedApiException is thrown rather than RateLimitExceeded by the TwitterErrorHandler.
The errorText returned from Twitter follows:
Rate limit exceeded. Clients may not make more than 350 requests per hour.
The rate limit should be checked using RateLimitStatus anyway so this problem can be predicted. .