I am using the UMIK-1 and Beta 45 as well. No issues on my end, however a couple of things that may help...
1) Does the umik-1 show up as available in other programs or in your OS controls/settings?
2) On Windows I have noticed that sometimes I need to restart REW to recognize device changes, especially if a device is disconnected for some reason.
3) Just to troubleshoot, have you tried to install ASIO drivers to see if that makes a difference?
4) Have you checked that the device is enabled in your OS (right click and enable). In windows, the shortcut is Windows+r 'mmsys.cpl' You can also try disabling and re-enabling here too.