I have exactly the same problem, although my setup is really fresh:
I am trialing Veeam and started with a fresh install of version 9 (22.214.171.1242), on WS2008R2. My host is a fresh install of full GUI, WS2012R2 with Hyper-V. I have a single VM guest, which is also 2012R2. I added the host to the Veeam Console successfully and noticed 3 components installed on my host (Veeam Backup Transport, Veeam Hyper-V Integration, Veeam Installer Service - all 126.96.36.1992).
When I created my first job, I added my host and left all other settings as default. When I run the job it fails with error "Unable to allocate processing resources. Error: On-host proxy [VHOST1] requires upgrade before it can be used."
When I look back at the 'Backup Infrastructure' tab, I see my host has been moved to Managed Servers > Microsoft Hyper-V > Unavailable. If I right-click this host the 'upgrade' option is greyed out.
I have an open support case #01709332. The engineer has already asked me to manually uninstall the components, remove the host, re-add the host, reinstall the components, but this did not fix the issue. I have also been advised to install the recommended hotfixes here https://www.veeam.com/kb1838
, but only one fix would install (KB3072380) - the others say "not applicable to your computer" when attempting to install - I guess that's because they relate to clustering, which is not what I'm using in my simple setup.
PS: I have a 'standard' trial license, so don't have ability to use WAN acceleration.
Any help advice greatly appreciated as this is eating into my license time.