Just installed Agent for Windows 13, get "Could not load file or assembly 'system.diagnostics.eventlog,

Installed on another system with new OS. (Win11 Pro)
This had no .net installed, so it installed it as part of the program install, runs fine.

So I removed all the .net instances on the first machine as well as Veeam agent, rebooted, reinstalled aganet, it needed to install .net and did so as part of the installation (I figured it would install the exact component needed) but still get the same error.
 

Check the logs here - %ProgramData%\Veeam\Endpoint Backup\Logs\

Otherwise I would suggest a support ticket to get to the bottom of this.

Looks like you’re on the right track ​@desertsailor according to these 2 posts I found on the error in:
https://learn.microsoft.com/en-us/answers/questions/1287135/(solved)-app-fails-with-could-not-load-file-or-ass

https://geekchamp.com/fix-could-not-load-file-or-assembly-or-one-of-its-dependencies-error/

See if the logs show anything more concrete as Chris suggests above. Something isn’t installing properly on the .Net side it appears.

Also...did you check the VAW v13 Sys Req’s?
https://helpcenter.veeam.com/docs/agentforwindows/userguide/system_requirements.html?ver=13

All the ancillary software installs (.Net Desktop, ASP.NET Core) need to be the same version. If you have any installed already and it’s a more recent version than VAW, Veeam will not install the version it has. And that means...if you didn’t/don’t have any of the other software required, Veeam will install it, but that would be a different version than what you have for the other software you already have. Make sense? All that to say..make sure all software is of equal version.

If it is...I don’t really have any other suggestion than Support.

While troubleshooting I discovered that I couldn’t view any of my eventviewer logs, they’d crash mmc. I figured since it seemed to be an “eventlog” type function, I cleared out all the logs and got the eventviewer back up and running. Uninstalled and reinstalled the Veeam agent, still the same error. I’ll follow up on the VAW v13 Sys Req’s next. Thanks.

All the system requirements are met, win11 25h2.

I’ll move towards a support ticket tomorrow. Thanks for all the input!

Let us know how it goes.