As the API is becoming very popular, more and more people are writing interfaces to it and some are very very bad. As some of the implementation do no caching, the API is getting hammered by some forums.
Because of this, we have had to add rate limiting (currently 1000 per day but thats not set in stone). This hasnt gone live yet but I will be checking how the mod will handle this.
Read more here
http://www.stopforumspam.com/forum/t573-Rate-Limiting