learner's block

The inability for a certain period of time to learn something, no matter how hard you try. When the block is broken, you are able to learn again.

Man, I couldn't get how to do this for an hour, but I must have had learner's block, because it was sooo simple.

learner's block

Inability to learn something, particularly due to psychological pressure. Often takes an existential threat to break.

From the first book of Harry Potter, and associated movie, comes this famous example:
Ron Weasley had a learner's block on Wingardium Leviosa, only broken during the toilet scene - he lifted the troll's club and KO'd the ugly thing.