Adobe Captivate license problem

Hi! My single license for Adobe Captivate CS6 let me install an app on two computers. I want to install the application on a third computer. I deactivated the application on the first computer yet. But when I try activate it on the new computer I have this problem: "the serial number is already in use by the maximum allowed computers. You need to deactivate another computer to use this product". Whats wrong?