dotnet/wpf · error · XamlParseException

SR.InvalidStartOfBaml

Error message

SR.InvalidStartOfBaml

What it means

BamlResourceDeserializer.LoadBamlImp throws this XamlParseException when the first node read from the BAML stream is not a StartDocument node. Valid BAML must begin with a document start; anything else means the stream is not BAML or is corrupt.

Solutions

1. Verify the stream contains compiled BAML (starts with BAML signature) not raw XAML text
2. Ensure the stream Position is 0 before deserializing
3. Rebuild the satellite/resource assembly to regenerate correct BAML
4. Check that the assembly producing the stream and the parsing code use compatible .NET/WPF versions

Example fix

// before
var deserializer = new BamlResourceDeserializer(xamlFileStream);
// after
xamlFileStream.Position = 0;
var deserializer = new BamlResourceDeserializer(compiledBamlStream);

// validate BAML magic before deserializing
var head = new byte[4]; stream.Read(head,0,4); stream.Position = 0;
if (head[0] != (byte)'B' || head[1] != (byte)'A' || head[2] != (byte)'M' || head[3] != (byte)'L') throw new IOException("Not a BAML stream");

try { tree = deserializer.LoadBaml(); } catch (XamlParseException ex) when (ex.Message.Contains("Baml")) { /* reload resource / rebuild assembly */ }

When it happens

Trigger: Deserializing a localization resource stream (via BamlLocalizer / BamlResourceDeserializer) whose bytes are not valid BAML — e.g. plain XAML text, wrong resource embedded, truncated or re-saved binary, or a stream positioned mid-file.

Common situations: Build misconfiguration embedding .xaml instead of compiled .baml; satellite assembly resource extraction bug; file corruption during copy/version mismatch between writer and reader; forgetting to seek the stream to position 0.

Understand the failure class

Background: Schema validation failed / invalid input schema: payload rejected because its shape doesn't match the expected schema — this error's family across 28 libraries.

Related errors

• SR.InvalidEndOfBaml
• SR.UnRecognizedBamlNodeType
• Can't Assign to Known Type attributes
• Could not find prefix for type
• Found unexpected Xmlns BAML record

AI-assisted analysis of dotnet/wpf@81131a70a4 (2026-09-14). Data as JSON: /api/errors/3cb37554a92bd29c. Report an issue: GitHub.

Appendix: source

Thrown at src/Microsoft.DotNet.Wpf/src/PresentationFramework/MS/Internal/Globalization/BamlResourceDeserializer.cs:52

        {
        }

        //-----------------------------
        // private  methods
        //-----------------------------
        /// <summary>
        /// build the baml element tree as well as the localizability inheritance tree
        /// </summary>
        /// <param name="bamlSteam">input baml stream.</param>
        /// <returns>the tree constructed.</returns>
        private BamlTree LoadBamlImp(Stream bamlSteam)
        {
            _reader = new BamlReader(bamlSteam);
            _reader.Read();

            if (_reader.NodeType != BamlNodeType.StartDocument)
            {
                throw new XamlParseException(SR.InvalidStartOfBaml);
            }

            // create root element.
            _root = new BamlStartDocumentNode();
            PushNodeToStack(_root);

            // A hash table used to handle duplicate properties within an element
            Hashtable propertyOccurrences = new Hashtable(8);

            // create the tree by depth first traversal.
            while (_bamlTreeStack.Count > 0 && _reader.Read())
            {
                switch (_reader.NodeType)
                {
                    case BamlNodeType.StartElement:
                        {
                            BamlTreeNode bamlNode = new BamlStartElementNode(
                                _reader.AssemblyName,

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