"Fms1/2 spd tgt diff"
This particular case is mentioned in the new fcoms in flight crew bulletins
It happens when changing the Crz FL using the altitude knob.
The new fcu altitude is sent by the master fmgc to the slave, therefore the predictions are not computed at the same time on both fmgc's, a speed difference may occur during a very short period, triggering the message.
Solution: diregard the message.