Double messages problem

Hello,

   Subscribers have recently started complaining that they are receiving multiple messages from the
mailing list, even though a check reveals that they are only subscribed once and have the same
subscriber settings as everyone else.
   
   Logs reveal that indeed some messages get sent to some subscribers twice - different SMTP ids,
but same MJ message id.

   I suspect something in MJ2 has become tripped up. Any suggestions or regular maintenence routine
that I may be missing that might fix this issue?

Thanks,
Alex