I do believe that your machine has a bad Vector Drive. The alarms that you mentioned are related to the DC buss voltage from the Vector Drive. These alarms are indicating that the DC buss voltage is too low for the machine to operate. The DC buss voltage output range is 305 – 355 with 325-330 DC being the nominal voltage.
I'll give you a few things to take a look at. You said that you checked the voltages and transformer taps. Nice. This is always the first thing you want to do when troubleshooting. Power up the machine and go to diagnostics (Press PARAM DGNOS twice) and then press the down arrow once to go to inputs 2 in diagnostics. You should see the DC buss voltage near the center of the screen. You said that that it takes 1.5-2 hours before the alarms will clear. My guess is that you will also see that the DC Buss voltage is too low on the screen during this time when the alarms occur. Test the actual DC Buss voltage at the Vector Drive. If the Drive is actually supplying good voltage, but what you see on the screen is too low, there is something wrong with the logic inside the Vector Drive and the only fix is to replace the drive.
This is how the system works: The mocon board is monitoring voltage from the Vector Drive. The mocon board recieves one volt for every 100 volts supplied to the DC Buss at P17. In other words, if the drive is generating 340 volts DC, it should normally send 3.4 volts to P17 on the mocon, which will display 340 volts on the screen in diagnostics.