Before trying an older version, I recommend downloading and re-installing the current version, then rebooting.
Especially when there aren't any similar reports, reinstalling the current version & rebooting often solves problems like these which come after an update install, either because the first install was corrupted in some way or because the problem came from something else that happened during the reboot which is then fixed by rebooting again.
Note: Do not uninstall first, since that would wipe your config. Just reinstall over the top.
It is also worth checking the installer to make sure it was not corrupted when it was downloaded.
If you do need to go back to a previous version, I have uploaded 10.5.0.0 here, assuming that is the version you were using before the 10.5.1.0 update:
32-bit: DOpusInstall-10.5.0.0.exe
64-bit: DOpusInstall-10.5.0.0-x64.exe
Another option is the latest beta version, 10.5.1.2, which you can find linked in my signature.