Error: Verification failed 3 times

Hello, since two days I get an error while releasing:

source.changes: 1k/2k550 Changes file must be signed with a valid GPG signature: Verification failed 3 times: ["(7, 1, u'General error')", "(7, 1, u'General error')", "(7, 1, u'General error')"] : Permission denied.
Note: This error might indicate a problem with your passive_ftp setting.
      Please consult dput.cf(5) for details on this configuration option.

I have no idea what I can do to fix this ...