If you have other digital phones and they are showing up same 01/01 12:00 am, then this might suggest core telephony has a problem. Select 'Identification' and ensure you see a country profile,such as UK. If not, you might need to do a cold restart of telephony, however this is a big deal - it will reset all your telephony configuration so you'll have to reconfigure it all again (else restore from a known good backup).
You could of course try the phone via one of the spare LAN connections (for example if you are using expansion 1 already, try the phone in the network port on the expansion unit).
Assuming it's just one i2004 with the problem, and all others are okay on this BCM, try it on another BCM50r1 and force a firmware download to it, then try it on this original BCM.
The last ever service update for 50r1 was BCM050.SU.SYSTEM.008_BCM50_1.0: BCM050.SmartUpdate.System.008-200806