[otrs] PGP Failed

Sirs, When I try to send email with PGP, doesn't work. See following logs. Jul 16 09:34:14 rt OTRS-CGI-10[31939]: [Error][Kernel::System::Crypt::PGP::Sign][Line:262]: Can't sign with Key 15279234: gpg: signing failed: file exists ! Anybody help me!