With PT3b2, and still with b3 I get an Old Database error when starting PT3 fresh off my desktop.
I have already hashed this out with Derek, but offer this to some of the others who might not find a quick easy fix.
When my PC cold boots, it loads postgreSQL but it may not be starting it. I am not versed enough to be sure one way or another.
When I invoke PT3, and get the 'Old Database error, I do this;
Start -> Programs -> PostgreSQL 8.2 -> Start Service.
A small DOS window appears, telling me the service is starting, then it goes away, and my PT3 is working.
Even if I hit OK, at the first 'Old Database' error, and PT3 come up, and it tells me there is a database error, I can do that simple fast procedure and then start importing and it has found the database.
This suggests to me that there might be the simple issue of the postgreSQL loading at boot, but never properly starting.
Try this and post results for both this error, and other database errors. This might be a really easy fix.