Puzzle 2552 gives an error popup, "files with unrecognized extensions specified: .otxt", and fails to open.
If another puzzle is already open, closing the popup returns to that puzzle.
If Foldit just started, closing the popup gives a blank screen. The hotkey ctrl+P opens the puzzle menu, allowing a different puzzle to be opened.
excerpt from log.txt:
standalone.application.boinc.Puzzle: {0} .opuzzle_setup 08586216d9939ed1b557037a98b94cc2
standalone.application.boinc.Puzzle: {0} .otxt 107b93705d69caecf631607419cda33f
standalone.application.boinc.Puzzle: {0} .owts 5b16284e5e5e4f85b6793eba788a0ce0
game.application.server.CurlFetcher: {0} https://fold.it/api/get_puzzle_scores
standalone.application.boinc.Puzzle: {0} has key .owts
standalone.application.boinc.Puzzle: {0} has key .opdb
standalone.application.boinc.Puzzle: {0} has key .opuzzle_setup
standalone.application.boinc.Puzzle: {0} Exception: Files with unrecognized extensions specified:
.otxt
in C:\Users\jflat06\foldit\develop\source\src\standalone\application\boinc\Puzzle.cc line 1983
It's happened before with this revisiting puzzle: https://fold.it/forum/bugs/unrecognized-extension-otxt
The errant file has been removed from the puzzle. It should be able to be loaded now. (Though you may have to close and reopen your client in order to get the updated file list for the puzzle.)