I'm trying to migrate Drupal 6 to Drupal 7 with Migrate d2d module. Problem is that I get 2 errors on Migrate dashboard page:

Decryption failed because the HMAC could not be validated.
Migration c9b87f5afFile could not be constructed.

And they are repeating many times. I can run migrate process, but custom defined field values are not migrated since I didn't map them. I can't access field mapping page because of this error.

Any idea how to resolve this?