Unsure of that error but there is a KB for agent install that might help - https://www.veeam.com/kb4507

Also you may want to search the forums too and see if there are reports there - https://forums.veeam.com

Hi Chris,

thank you very much for your help. I really appreciate it!

I don´t think KB4507 is the solution for my issue, because I don´t get this Windows Installer Window that is shown in this KB. But I will try it anyway because I have no further ideas.

I can´t find any similar issue in the forum, the only similiar issue I could found in the forum is this one.
But there is no solution so far.

Best regards
Daniel

If there is not solution yet for the forum post I might suggest opening a support ticket for further assistance as that may be the best course of action at this point.

Yes, but it´s Community Edition.
I have no hope getting an answer.

Regards
Daniel

Well you can only try as this is the community and not support so we can only help to our best ability.  Also support does not come on here.  Hopefully you will get an answer from support.

I’ll install the agent locally on the guest sometimes for stubborn physicals. You may have better luck redeploying the agent locally with an elevated prompt vs pushing it. 

That is a good suggestion as well to try.

I would echo Chris’ recommendation of opening up a ticket with support.  Obviously it’s going to be best effort since you’re using CE, but they may still be able to help.  Another option of course would be to purchase a license to include paid support.

Personally, it sounds like a full manual uninstall or database reset may be required on the machines running the agent.  I did a quick google search and found the below link in the forums, but it doesn’t likely entirely apply here, but that would be the direction I’d probably be looking at if you’ve remove the agents already but can’t redeploy them. 
https://forums.veeam.com/servers-workstations-f49/case-05066933-need-to-manually-uninstall-every-trace-of-agent-t77130.html

I had an issue recently where the agent was still attempting to tie back to the previous backup server when I had to rebuild for a client.  I ended up not reinstalling the agent, but did have to issue some commands to allow the agent to be managed by the new server.  I plan on posting a blog about it soon, but the doc that got me on the right path is below.
https://helpcenter.veeam.com/docs/agentforwindows/configurator/setvbrsettings.html?ver=60
 

First of all, I would like to thank everyone who has taken the time to reply here to find a solution.

I have now been able to solve the issue and I will share the information if anyone else has the same error message.

Why did this error appears?
I think it was an incompatibility between the agent and the Veeam B&R because of the new installation of B&R. Before the PostGre database crashes, I used an older version of B&R. Then I uninstalled this version, downloaded the latest version and installed it. After the installation and import the configuration file, I got this error messages.

How did I solve it?
First of all, I uninstalled all Agents on the servers to start from scratch.
Then I uninstalled B&R and installed a clean version of B&R once again. Before I imported the configuration file, I created a Backup Job only with the servers, that had the agent installed, but I didn´t started the Job. Then I rescanned the Physical Infrastructure and Veeam B&R installed the latest version of the Agent on these servers. After successfull installation of the agents, I removed the Backup Job and the configuration from the physical infrastructure. Then I imported the configuration file and everything was fine. Veeam B&R didn´t display any error messages and continued the backup jobs where it stops.

Best regards
Daniel

Glad to hear you were able to resolve and fix the issue.  Thanks for sharing the solution.