This can indicate a failure in the transponder, but not always.
The DPSK Unlock message would normally be caused by an issue with the transponder module, and is there to make you aware that you are no longer replying to interrogations.
However, if the unit is still replying (ATC do not complain about him disappearing from radar) then this is a false trigger of the warning, caused by electrical interference in the aircraft. We have seen this only a couple of times in the field. But if this is the case, swapping the transponder won't relieve the symptom, as the false triggering continues.
In short, you might want to look at adding Ferrite beads on the RS232 communication lines/upgrade to shielded twisted pair/check shielding/move the base unit away from sources of radio frequency interference.
Give our support team a call at 425-402-0433 or support at dynonavionics dot com if you'd like more help with this issue.