If you finish a set of unlearned words and new words show up to be learned, in many cases you are seeing MemriseLearnableSourceError error 101. Either the new client can’t talk to the server properly or the server is malfunctioning, but this started two days ago.
This makes it impossible to continue with certain courses.
It would be better to actually show something more meaningful in the error message for proper resolving of issues. See screen shot below.
PS: You should really run regression tests, it seems each new update causes things to break.