What causes "Failed to unregister: {ex.Message}" in CoplayDev/unity-mcp?

Read the InnerException.Message for the underlying cause (IO, parse, or null-ref).

CoplayDev/unity-mcp · error · InvalidOperationException

Failed to unregister: {ex.Message}

Error message

Failed to unregister: {ex.Message}

What it means

JsonFileMcpConfigurator.Unregister() parses the client config file, removes the unityMCP key from its container (mcpServers/servers/mcp), and writes it back. Any exception during this read-parse-remove-write cycle is caught and re-thrown as InvalidOperationException with a 'Failed to unregister:' prefix. The original exception is preserved as InnerException.

Source

Thrown at MCPForUnity/Editor/Clients/McpClientConfiguratorBase.cs:413

                }
                else
                {
                    string containerKey = string.IsNullOrEmpty(client.ServerContainerKey)
                        ? "mcpServers" : client.ServerContainerKey;
                    if ((root[containerKey] as JObject)?.Remove("unityMCP") == true) removed = true;
                }

                if (removed)
                {
                    File.WriteAllText(path, root.ToString(Formatting.Indented));
                }

                client.SetStatus(McpStatus.NotConfigured);
                client.configuredTransport = Models.ConfiguredTransport.Unknown;
            }
            catch (Exception ex)
            {
                throw new InvalidOperationException($"Failed to unregister: {ex.Message}", ex);
            }
        }

        public override string GetManualSnippet()
        {
            try
            {
                string uvx = GetUvxPathOrError();
                return ConfigJsonBuilder.BuildManualConfigJson(uvx, client);
            }
            catch (Exception ex)
            {
                var errorObj = new { error = ex.Message };
                return JsonConvert.SerializeObject(errorObj);
            }
        }

        public override IList<string> GetInstallationSteps() => new List<string> { "Configuration steps not available for this client." };

View on GitHub (pinned to c21bf496bc)

Solutions

Read the InnerException.Message for the underlying cause (IO, parse, or null-ref).
Close any editor that has the config file open, then retry Unregister.
Validate the config file JSON with a linter and fix syntax errors.
Check filesystem permissions on the config directory and file.
If the file is corrupt beyond repair, back it up, delete it, and re-Configure.

Defensive patterns

Strategy: try-catch

Validate before calling

string path = GetConfigPath();
if (!File.Exists(path)) { /* nothing to unregister */ return; }
string text = File.ReadAllText(path);
JToken.Parse(text); // validate parse before Unregister

Try / catch

try { configurator.Unregister(); }
catch (InvalidOperationException ex)
{ Debug.LogError($"Unregister failed: {ex.Message}. Inner: {ex.InnerException?.Message}"); }

Prevention

Close config files in other editors before unregistering.
Validate JSON before triggering unregister operations.
Check the InnerException for the root cause of IO or parse failures.

When it happens

Trigger: File IO errors (permissions, disk full, file locked by another process), JSON parse errors on a corrupt config file, or an unexpected null during JObject traversal.

Common situations: The config file is open in another editor that locks it. The user has a malformed config file from a manual edit. Antivirus or sync software (Dropbox, OneDrive) is temporarily locking the file. Disk full or read-only filesystem.

Related errors

AI-assisted analysis of CoplayDev/unity-mcp@c21bf496bc (2026-08-13). Data as JSON: /api/errors/78b69bad710b96cf. Report an issue: GitHub.