Please provide the exact error you're seeing. CBs errors are as follows.
Key: UE_NOT_AUTHORIZED
Text: You are not authorized to view this page!
Key: ERROR_PASS
Text: Sorry, no corresponding user was found
Key: EXCEEDED_MAXIMUM_PASSWORD_RESETS
Text: You have exceeded the maximum number of password resets allowed. Please try again in 1 hour.
Those are the only errors that CBs forgot login behavior can output for password resetting outside of user object store errors.
If you've any auto actions acting on user update events you may want to also check those and to quickly test if that could be the issue I recommend unpublishing CB Auto Actions then retrying.