How to Fix RPC Errors in Claude Cowork on Windows

While trying to use Claude's Cowork (desktop app), I ran into this error:

RPC error -1: failed to ensure virtiofs mount: Plan9 mount failed: bad address

I had no idea what this meant, so I did some digging. Here's what I found and what worked.

The Short Answer

This is a known bug in the Windows version of Cowork that tends to occur when certain conditions overlap. In most cases, restarting the app or changing the working folder resolves it.

Steps to Try

1. Restart Claude Desktop

Fully quit Claude Desktop and restart it. This alone can fix the issue in some cases.

2. Change Your Working Folder

The folder you've selected might be causing the problem. Avoid folders like these:

Instead, create a plain local folder like C:\Users\YourName\Documents\work and point Cowork to that.

In my case, this fixed the issue. The root cause was that I had selected a folder managed by OneDrive.

3. Check Hyper-V Related Features

Open "Turn Windows features on or off" and verify that the following two features are enabled:

If they're disabled, enable them and restart your PC.

Under the hood, Cowork uses virtiofs (a virtual file system) to mount host-side folders. Without these virtualization features enabled, the mount operation fails.

4. If Nothing Works

There are multiple reports on Anthropic's official GitHub that this issue is especially common with the Windows 11 Home + Team plan combination. As of now, it's a known issue awaiting a fix, and the Anthropic team is working on it.

You can submit feedback through the Claude Desktop settings screen or by using the thumbs-down button in the chat interface.

Summary

Start with the cause that most closely matches your situation. Behavior can vary depending on your OS edition (Home/Pro) and subscription plan, so checking those details can help narrow things down if you can't reproduce the issue.