2001 Prius: P3002 OBD II Code

I just got an OBD II reader and ran it through its diagnostic program on a 2001 Prius (my gf's.) The 2 error codes I received are:

P0420 (Catalytic convertor problem or something; this I'll fix and is not the point of this thread.)

P3002: I have no idea what this is, Googled and it seems to be HV ECU Communication failure.

Some facts about the car:

- This car has about 120,000 miles,
- Was bought from the original owner at about 110,000 miles earlier this year (my gf's the 2nd owner.)
- Clean title, never been in an accident (if you don't count hitting the car in front at < 0.5mph when parallel parking.)
- Has never had any serious problems come up since owning it.
- Been a little behind on the maintenance, only maintenance done was oil changes every 4000-5000 miles, changing the drive belt, fixed some steering problem (got a Toyota recall notice for that), and tire rotations.

How serious is this error and is immediate attention needed in the near (or far) future?