Error 518 "Your application has exceeded usage limit on this call", but I'm well under the limit??

[dasherdeals]

I'm running ~30 GetMyeBaySelling calls every 5-15 minutes.
Documentation states:  "Per (seller) user ID, no more than 300 GetMyeBaySelling calls can be executed within any 15-second interval."

As of today, I can't call it at all. 
Error 518 "Your application has exceeded usage limit on this call, please make call to Developer Analytics API to check your call usage." 

Making a call to the Developer Analytics API responds with no limits reached.
What gives?

Thanks in advance!