Unity-Technologies/UnityCsReference · error · ArgumentException

Unable to add '{sourceFile}' to StreamingAssets. An entry fo

Error message

Unable to add '{sourceFile}' to StreamingAssets. An entry for '{targetPath}' has already been added, '{existingValue}'.

What it means

Thrown by BuildPlayerContext.AddAdditionalFileToStreamingAssets when a file is added for a targetPath that already has a different source file registered. The StreamingAssetFiles dictionary maps target paths to source files; a second registration under the same target with a different source is treated as a conflict. Adding the identical file twice is silently ignored.

Source

Thrown at Editor/Mono/BuildPipeline/BuildPlayerContext.cs:108

                NPath targetPath = pathInStreamingAssets ?? sourcePath.FileName;
                AddAdditionalFileToStreamingAssets(sourcePath, targetPath);
            }
            else
            {
                throw new FileNotFoundException("No such file or directory.", sourcePath.ToString());
            }
        }

        private void AddAdditionalFileToStreamingAssets(NPath sourceFile, NPath targetPath)
        {
            if (StreamingAssetFiles.TryGetValue(targetPath, out var existingValue))
            {
                // If someone is adding the same file more than once we ignore subsequent adds
                if (existingValue == sourceFile)
                    return;

                // Throw an exception and tell the user what the problem is
                throw new ArgumentException(
                    $"Unable to add '{sourceFile}' to StreamingAssets. An entry for '{targetPath}' has already been added, '{existingValue}'.");
            }
            StreamingAssetFiles.Add(targetPath, sourceFile);
        }
    }
}

View on GitHub (pinned to 225b0fbdb5)

Solutions

1. Ensure each targetPath is unique across all AddAdditionalFileToStreamingAssets calls — namespace by feature or subfolder if needed.
2. If two sources legitimately need the same name, place them in different subdirectories under StreamingAssets.
3. Audit all AddAdditionalFileToStreamingAssets callers (including third-party plugins) to find the conflicting registration.

Example fix

// before
context.AddAdditionalFileToStreamingAssets("config/dev.json", "settings.json");
context.AddAdditionalFileToStreamingAssets("config/prod.json", "settings.json"); // conflict!

// after
context.AddAdditionalFileToStreamingAssets("config/dev.json", "dev/settings.json");
context.AddAdditionalFileToStreamingAssets("config/prod.json", "prod/settings.json");

static readonly HashSet<string> s_registeredTargets = new();

void AddToStreamingAssetsUnique(BuildPlayerContext ctx, string sourcePath, string targetPath)
{
    if (s_registeredTargets.Contains(targetPath))
        throw new ArgumentException(
            $"Duplicate StreamingAssets target '{targetPath}'. Use a unique subfolder.");
    s_registeredTargets.Add(targetPath);
    ctx.AddAdditionalFileToStreamingAssets(sourcePath, targetPath);
}

When it happens

Trigger: Two calls to AddAdditionalFileToStreamingAssets that map different source files to the same target path inside StreamingAssets — e.g., adding 'config/local.json' and 'prod/config.json' both as 'config.json'.

Common situations: Multiple build processors or plugins each adding files to StreamingAssets without coordinating target paths, a loop that adds files with a fixed target name, or two features both wanting 'settings.json' at the StreamingAssets root.

Related errors

• No such file or directory.
• Scene path "{0}" contains invalid directory separators.
• The build target does not support build appending.
• The build cannot be appended.
• Non-development build cannot allow debugging. Either add the

AI-assisted analysis of Unity-Technologies/UnityCsReference@225b0fbdb5 (2026-08-13). Data as JSON: /api/errors/3e75db0a408ae6f6. Report an issue: GitHub.