[otrs] an error message in the system log

Hi All! The following error message is in the system log: error OTRS-CGI-10 Another Link already exists within the same type group! What does it mean? Maybe (!, because the agent notify me later) an agent want to answer to multiple tickets with the bulk action, and she says that no email was sent out. We have groups and subgroups ... Maybe is this the problem? Thanks Krisz