If you seem to be stuck in a lesson, there are several reasons and steps for resolution:

• Your browser may have been disconnected from the server.  This is an issue where bandwidth is too low for the numbers of users connected (NativeAccent requires 30Kbits/s per user to the cloud) OR when there is a faulty or misconfigured device (switch, router, proxy server, or firewall) in the data path.  Contact your local network support.
• You may be saying the word too quickly or too slowly. There is an element of duration as well as pronunciation that effects grading.  Listen to the model speaker and to your recording. 
• Distortion of the sound (your breath, background noise, etc) will affect the accuracy of the speech recognition system. Listen to the model speaker and to your recording. 
• f you do not get the exercise correct in about 5-10 tries, the system will move you forward to the next exercise. There is a large amount of curriculum in the program, and you will acquire that skill from other exercises.