## TL;DR

The 1.5.0 migration added a uniqueness constraint on file.name that broke the MCP component in SSE mode, surfacing as a Superuser account error. The real fix is in 1.6.0, which removes that constraint on upgrade, so upgrading to 1.6.0 resolves it for both clean installs and upgrades.

## Steps

1. The 1.5.0 migration added a uniqueness constraint on file.name that broke the MCP component in SSE mode, surfacing as a Superuser account error. The real fix is in 1.6.0, which removes that constraint on upgrade, so upgrading to 1.6.0 resolves it for both clean installs and upgrades. The maintainer confirmed this directly and the reporter agreed to try the upgrade.

Expected: The maintainer confirmed this directly and the reporter agreed to try the upgrade.

## When to use

You are seeing this: After upgrading to Langflow 1.5.0, the MCP Tool block stopped working in SSE mode. Use this skill when you run into "Langflow MCP component build error in SSE mode after 1.5.0 upgrade (Superuser error)".

## When not to use

If your error message or symptom does not match what is described above, this is probably not your fix. Search for your exact error text instead of forcing this one to fit.

## Versions

Versions mentioned in the source: Langflow 1.5.0, 1.6.0. If you are on something much newer or older, the details may have shifted.

## Why this happens

The original report does not dig into a root cause. It documents the symptom and the fix that resolved it.