bug: MCP filesystem server fails with "os error 267" (directory name invalid) — works in upstream Jan

[MarcLocalAI]

Version: v2.0.23

Describe the Bug

The @modelcontextprotocol/server-filesystem MCP server fails to start with "The directory name is invalid. (os error 267)" on every launch attempt, regardless of configuration. The identical server config works correctly in Jan (the upstream project this was forked from) on the same machine.

Steps to Reproduce

1. Add an MCP server (STDIO transport) with:
   • Command: npx
   • Args: -y, @modelcontextprotocol/server-filesystem@2026.1.14, C:\Users\Marc\Documents\Test1
2. Save and attempt to connect.
3. Observe: Failed to run command filesystem: The directory name is invalid. (os error 267)

Already ruled out:

• Running the identical command manually in PowerShell works fine
• Target folder exists and was verified before each test
• Tested path with and without spaces — same error
• Tested Command as bare "npx", full path "C:\Program Files\nodejs\npx.cmd", and routed through "cmd /c" — same error every time
• Tested with and without the @2026.1.14 version pin — same error
• Added APPDATA and USERPROFILE as explicit Environment Variables in the server config — same error
• Confirmed npx.cmd and node.exe both exist in C:\Program Files\nodejs
• npm config list shows no unusual prefix/cache paths

Key finding: identical config connects and runs successfully in Jan on the same machine — points to a regression in Atomic Chat's fork rather than a config issue. os error 267 is Windows' ERROR_DIRECTORY, which typically means an invalid working directory was passed to process creation — possibly unrelated to the Args shown in the UI. A similar root cause was reported in another Tauri/Electron AI client: aofp/yume#12

Screenshots / Logs

[14:40:49] INFO Starting MCP server filesystem (Initial attempt)
[14:40:49] ERROR Failed to run command filesystem: The directory name is invalid. (os error 267)
[14:40:49] WARN Failed to start MCP server filesystem on first attempt: Failed to run command filesystem: The directory name is invalid. (os error 267)

Operating System

• MacOS
• [✔️] Windows - Windows 11 Pro
• Linux

[Vect0rM]

Thank you for such a thorough report — the os error 267 diagnosis was spot on and saved us a lot of digging.

Here's what we found. Atomic Chat adds an optional Working directory (cwd) field to STDIO MCP servers (it's under "Show advanced" in the server dialog, and the bundled filesystem entry ships with one pointing at Documents\Atomic_chat). That value was handed straight to the process launcher without checking it exists, so if the folder is missing, moved, or the path is otherwise invalid, Windows refuses to start the process with ERROR_DIRECTORY (267). Upstream Jan doesn't have this field at all, which is exactly why the same config works there.

The fix is coming in the next release: the working directory is validated before launch, and if it isn't an existing folder the server starts from the default location with a warning in the log instead of failing.

In the meantime, a workaround: edit the server → Show advanced → clear the Working directory field (or remove the "cwd" key from mcp_config.json), and it should connect.

We truly appreciate your help in making Atomic Chat better!