What you were expecting to happen, and what actually happened?
Finished the last challenge, Under the Sea, of Merlantis at normal difficulty. Instead of going to the rewards I get an internal error prompt and I am back on the map.
What are the steps to make it happen again?
Finish the challenge and wait for the error. Tested it 3 times.
Do you have any screenshots or video you want to share with us so we can see the problem? Attach them to your post!
Recorded on PC running the game from Steam on Win7.