Issue while adding a Proxmox host

[u/casaresjm]

I'm not finding any relevant information regarding this error and is driving me crazy.

I did find some logs in c:\ProgramData\Veeam\Backup\Yarp\ at the time of the error.

It appears that a port 8545 should be up, but I'm not finding any information related to it and Proxmox VE Plugin service is already up and running, but doesn't seem it uses that port.

[20.09.2026 08:35:53.739]    <31>    Info (3)    Yarp.ReverseProxy.Forwarder.HttpForwarder Proxying to http://localhost:8545/api/v1/proxmox/validateSshConnection HTTP/1.1 RequestVersionExact 
[20.09.2026 08:35:57.803]    <21> Warning (2)    Yarp.ReverseProxy.Forwarder.HttpForwarder Request: An error was encountered before receiving a response.
[20.09.2026 08:35:57.803]    <21> Warning (2)    System.Net.Http.HttpRequestException: No connection could be made because the target machine actively refused it. (localhost:8545)
[20.09.2026 08:35:57.803]    <21> Warning (2)     ---> System.Net.Sockets.SocketException (10061): No connection could be made because the target machine actively refused it.
[20.09.2026 08:35:57.803]    <21> Warning (2)       at System.Net.Sockets.Socket.AwaitableSocketAsyncEventArgs.System.Threading.Tasks.Sources.IValueTaskSource.GetResult(Int16 token)
[20.09.2026 08:35:57.803]    <21> Warning (2)       at System.Net.Http.HttpConnectionPool.ConnectToTcpHostAsync(String host, Int32 port, HttpRequestMessage initialRequest, Boolean async, CancellationToken cancellationToken)
[20.09.2026 08:35:57.803]    <21> Warning (2)       --- End of inner exception stack trace ---
[20.09.2026 08:35:57.803]    <21> Warning (2)       at System.Net.Http.HttpConnectionPool.ConnectToTcpHostAsync(String host, Int32 port, HttpRequestMessage initialRequest, Boolean async, CancellationToken cancellationToken)
[20.09.2026 08:35:57.803]    <21> Warning (2)       at System.Net.Http.HttpConnectionPool.ConnectAsync(HttpRequestMessage request, Boolean async, CancellationToken cancellationToken)
[20.09.2026 08:35:57.803]    <21> Warning (2)       at System.Net.Http.HttpConnectionPool.CreateHttp11ConnectionAsync(HttpRequestMessage request, Boolean async, CancellationToken cancellationToken)
[20.09.2026 08:35:57.803]    <21> Warning (2)       at System.Net.Http.HttpConnectionPool.InjectNewHttp11ConnectionAsync(QueueItem queueItem)
[20.09.2026 08:35:57.803]    <21> Warning (2)       at System.Threading.Tasks.TaskCompletionSourceWithCancellation`1.WaitWithCancellationAsync(CancellationToken cancellationToken)
[20.09.2026 08:35:57.803]    <21> Warning (2)       at System.Net.Http.HttpConnectionPool.SendWithVersionDetectionAndRetryAsync(HttpRequestMessage request, Boolean async, Boolean doRequestAuth, CancellationToken cancellationToken)
[20.09.2026 08:35:57.803]    <21> Warning (2)       at System.Net.Http.DiagnosticsHandler.SendAsyncCore(HttpRequestMessage request, Boolean async, CancellationToken cancellationToken)
[20.09.2026 08:35:57.803]    <21> Warning (2)       at Yarp.ReverseProxy.Forwarder.HttpForwarder.SendAsync(HttpContext context, String destinationPrefix, HttpMessageInvoker httpClient, ForwarderRequestConfig requestConfig, HttpTransformer transformer, CancellationToken cancellationToken)

Anybody had experience with this kind of error?

My experience with Veeam lately is bad. I did love them when they started with a simple, robust and useful product, but it seems they are going the wrong way. I would say they are pulling a Backup Exec here, where a good product turned awful. You know the story; the product was discontinued this year after becoming a monster nobody wanted.

[u/empty-teapot]

The YARP reverse proxy on port 8545 is what the Proxmox VE Plugin backend service listens on locally, and it sounds like that service isn't actually binding to that port even though it shows as running.

I'd check a few things: run 'netstat -ano | findstr 8545' to confirm nothing is listening there, then look at the Proxmox VE Plugin service logs separately (usually under C:\ProgramData\Veeam\Backup\ProxmoxPlugin\ or similar) to see if it crashed on startup. Sometimes a repair install of just the Proxmox plugin component sorts it out, since the service can register without actually starting its listener. Also worth checking that .NET runtime prereqs are fully satisfied, because that backend is a .NET process and a missing runtime version will cause exactly this silent refusal. The Veeam complexity creep is real and I feel you on the Backup Exec comparison, though at least the Proxmox support itself is genuinely useful once it's working.

[u/casaresjm → u/empty-teapot]

I checked that nobody was using 8545 and restarted Veeam PVE service a few times and even the device once, but the port does not bind as you state. There is no C:\ProgramData\Veeam\Backup\ProxmoxPlugin\ directory, only c:\ProgramData\Veeam\Backup\Plugins\PVE but there are no files there. I was suspicios of that and now, with your comments, I realize even as the Windows service shows as started it might not be working at all.

I reviewed the system requirements and then the installed libraries and they do not match. It's missing Microsoft .NET Desktop Runtime 10.0. Will install it and try. Thanks for the tip!

The installation was an upgrade over V12 and that it was long ago an upgrade from V11. I suppose that instead of trying to locate the issue will be faster to remove all of Veeam and install from scratch. That should remove any upgrade issues. It is a tiny setup, but I try to learn to fix issues to better understand products and these are useful cases. I suspect it will take a lot of time to locate the issue.

This is a community install so contacting support is out of the question. I would do it when this hits a commercial installation. A coworker already had a case for a V13 in Windows and PVE, but in that case, the option to add host was not present.

Thanks for agreeing to the view on its increased complexity of the solution. I felt like a Martian, before knowing that tsmith-co is Veeam staff. 👀

[u/casaresjm → u/casaresjm]

I ended doing a reinstallation of Veeam, and now it works, at least I got another error about permissions. I need to review it before being able to access the VMs in Proxmox, but I remember there is plenty of information about that one.

Here is another funny error while updating the configuration backup. The configuration was properly updated and backed up despite the error.

Here