We have been experiencing some high usage of our free service. From tomorrow morning we'll start banning users who have exceeded the 3000/day limit consistently over the last month. This should rectify the issue for low use users, but it will completely block many others.
If you are dependent on this system, then I strong suggest migrating to our cloud base platform. Details of which can be found here: http://www.codecogs.com/latex/licence.php