BDCs & PDC does not synch automatically

One possible reason is that the secure channel between the PDC and BDC has failed. The TechNet articles I've read on this recommend recreating the machine account for the BDC as follows:
1. On the PDC in Server Mgr., create a new machine account with a different name.
2. On the BDC, change the computer name to the name of the new machine account you created and then reboot and log on to the domain using the new machine name. (You must be logging on to the same domain as the PDC, not a trusted domain.)
3. Synchronize the entire domain manually from Server Manager. At this point, the BDC should be able to synchronize properly.
4. On the PDC, in Server Manager, delete the old machine account (the BDC's old computer name).
5. Synch the entire domain again manually and make sure the old BDC name no longer appears in Server Manager. This may take 10-15 minutes sometimes.
6. After the old BDC name is gone from Server Manager, recreate an account with the old BDC name, and then again manually synch the entire domain.
7. Go back to the BDC, change the name back to the old name, shut down and restart, and log back on to the domain.
8. Resynch the entire domain manually again - this time the BDC should synch with its oldname.
9. On the PDC, remove the temporary machine account you created for the BDC.

Hope this helps!

The root cause is the database synchronization process itself. By default, these synchs are separated by a time factor so that not all of a PDC's time is spent doing them. You can get around this by editing the registry (which is a lengthy process) or by manually synching the databse yourself as you make the changes. If you are at the BDC, simply choose start/programs/administrative tools common/server manager. Hilight the BDC, click computer on top left of tool bar, and choose "synchronize with primary domain controller" If you would like the registry hack, please email me at the above address.
Good luck!

Mike

ps. increasing the synch time through the registry will only decrease the performance of anything else your server does andof the network itself as the entire database copies over. Default time for any change is 50 minutes maximum.