Rider crashes at launch after update: backend exit code 77, missing NuGet.Core.dll

Problem

JetBrains Rider fails to start after an update. On launch it shows a crash prompt that asks for the zipped log folder to be sent to support. In the logs, the backend process (Rider host) starts and exits immediately with exit code 77, and the IDE relaunches it repeatedly.

Frontend log (idea.log):

2026-07-22 09:09:47,430 [   2707]   SEVERE - #c.j.r.p.ReSharperProcessBase - Rider host (PID = 26348) has unexpectedly exited with exit code 77.

Backend log (backend.log):

|E| JetEnvironment | Could not run the application environment. The task has failed. The handler “{myDeployedPackages=<NULL>,myMinimalPackageSetFilter=<NULL>,myProductBinariesDirArtifact=“C:\Program Files\JetBrains\JetBrains Rider 2023.3.3\lib\ReSharperHost”}” failed to yield the full part catalog set. Failed to calculate Product Binaries Dir Packages Set Identity. The type initializer for 'JetBrains.Application.BuildScript.Solution.AllAssembliesLocator' threw an exception. The type initializer for 'JetBrains.Util.Storage.Packages.NugetHelpers' threw an exception. Could not load file or assembly 'NuGet.Core, Version=2.14.0.19086, Culture=neutral, PublicKeyToken=5aaa11a165479571'. The system cannot find the file specified.

Cause

NuGet.Core.dll, a library that ships with Rider, is missing from the installation directory (<Rider installation>\lib\ReSharperHost). Without it, the backend cannot build its product-binaries package catalog during startup, so the application environment fails to initialize and the process exits with code 77.

Common triggers:

• An interrupted or partial update that leaves the installation in an inconsistent state. In one reported case a 2026.2 build ran from a folder still named JetBrains Rider 2023.3.3.
• Antivirus software quarantining the bundled NuGet.Core.dll.

Resolution

1. Reinstall Rider with the JetBrains Toolbox App, or uninstall and install it again. Remove any leftover older installation folder (for example, C:\Program Files\JetBrains\JetBrains Rider 2023.3.3) so that no mixed files remain. From the installed Rider version go to Help > Delete Leftover IDE Directories or find locations of the Rider directories here: Directories used by the IDE
2. Check whether antivirus software has quarantined NuGet.Core.dll in <Rider installation>\lib\ReSharperHost. If it has, restore the file and add the Rider installation directory to the antivirus exclusions.