Having trouble with Urbackup and WIN_XP/SERVER_03 after 2.x update

We have one location with a Urbackup Server running on Ubuntu Server 14.04.4. The NIC popped on the Server, so I replaced the server. The previous server was running off of the 1.4 release I believe. I setup the new Server with the 2.x release. I tried installing the new client on a few legacy 2003 Servers we have, but it would error out saying that Server 2003 and XP were no longer supported. I then installed the 1.4.11 client on those legacy workstations/servers, and it installed and found the server. Now, though, if I try to access the web gui for Urbackup it says that it has to rebuild the database. Can I have the 1.4 and 2.x clients running off of the same server? Do I need to use the old urbackup-server version to back up legacy WIN OS PCs too?

P.S. This software has been amazing though. Have thoroughly enjoyed using it, and it definitely has been a lifesaver. Thanks Uroni on your work!

Here 1.4 clients work with 2.x server here. (It seems like first incremental backup was full backup though, think because of hashing)

I got v2.0.30 client to work on XP too, but not sure how safe it is yet
(have it on a few workstation to test, for now it seems to work fine)