You may receive a "Document Locked" error message in the BizTalk Server 2004 error log when you save an InfoPath document directly to a Windows SharePoint Services site

// The following function handler is created by Microsoft Office InfoPath. Do not
// modify the type or number of arguments.
[InfoPathEventHandler(EventType=InfoPathEventType.OnSubmitRequest)]
public void OnSubmitRequest(DocReturnEvent e)
{	
	// If the submit operation is successful, set
	// e.ReturnStatus = true;
	// Write your code here.

	// Create an XmlDocument object from the MSXML 5.0 object.
	System.Xml.XmlDocument doc = new System.Xml.XmlDocument();
	string xml = this.thisXDocument.DOM.xml;
	doc.LoadXml(xml);

	bool success = false;
	// The URL of the following file can be computed from the Outbox URL.
	// The Outbox URL can be retrieved by invoking the TPPubWS.GetOutboxDocumentLibraries method that is defined
	// in the TPPubWS Web service. For additional information, see the BizTalk Server 2004 documentation.
	success = PutUtf8File(xml,"http://<servername:serverport>/sites/BASSite/Outbox/Form2.xml", false);
	e.ReturnStatus = success;
}

/// <summary>
/// The method uses WebDAV protocol to create a file at the specified URL.
/// The code performs an HTTP PUT Web request to create an UTF-8 encoded XML file
/// at the specified location on the Windows SharePoint Services site.
/// </summary>
/// <param name="utf8XmlDoc">XML document that has the encoding attribute set to "UTF-8" or has no encoding attribute at all.</param>
/// <param name="fileUrl">The URL where the document will be created. It must include the file name.</param>
/// <param name="overwrite">Set the value to true to overwrite the existing file or false to fail if a file that has the same URL exists.</param>

public static bool PutUtf8File(string utf8XmlDoc, string fileUrl, bool overwrite)
{
	// HTTP Headers are used to control the overwrite behavior for HTTP PUT.
	const string IfNoneMatchHeader = "If-None-Match"
	const string IfNoneMatchValue = "*"

	byte[] Buffer = null;
	byte[] Preamble = null;

	Stream outputFile = null;
	HttpWebResponse Response = null;
	HttpWebRequest PostFile = null;
	HttpStatusCode statusCode = HttpStatusCode.ServiceUnavailable;

	try
	{
		UTF8Encoding encoder = new UTF8Encoding();
		Preamble = encoder.GetPreamble();
		Buffer = encoder.GetBytes(utf8XmlDoc);

		PostFile = (HttpWebRequest)WebRequest.Create(fileUrl);
		PostFile.Method = "PUT"
		if (!overwrite)
		{
			// Do not overwrite existing files.
			PostFile.Headers.Add(IfNoneMatchHeader, IfNoneMatchValue);
		}
		// Use the client credentials when you save the file.
		PostFile.Credentials = CredentialCache.DefaultCredentials;

		// The content length must be set before you start to write data.
		PostFile.ContentLength = Preamble.Length + Buffer.Length;
		outputFile = PostFile.GetRequestStream();

		// Write the byte order mark.
		outputFile.Write(Preamble, 0, Preamble.Length);
		outputFile.Write(Buffer, 0, (int)Buffer.Length);

		if (outputFile != null)
		{
			outputFile.Close();
			outputFile = null;
		}
		if (PostFile != null)
		{
			Response = (HttpWebResponse)PostFile.GetResponse();
			statusCode = Response.StatusCode;
		}
	}
	catch(System.Net.WebException we)
	{
		Response = we.Response as HttpWebResponse;
		statusCode = Response.StatusCode;
	}
	finally
	{
		if (outputFile != null)
			outputFile.Close();
		if (Response != null)
			Response.Close();

		PostFile = null; // No Close or Dispose method exists for this object.
	}

	if ((statusCode == HttpStatusCode.OK) || (statusCode == HttpStatusCode.Created))
	{
		return true;
	}
	else if (statusCode == HttpStatusCode.PreconditionFailed)
	{
		// The file already exists.
		return false;
	}
	else
	{
		// An error was encountered.
		return false;
	}

}

//=======
// The following function handler is created by Microsoft Office InfoPath.
// Do not modify the name of the function, or the name and number of arguments.
//=======

function XDocument::OnSubmitRequest(eventObj)
{
	// If the submit operation is successful, set
	// eventObj.ReturnStatus = true;

	var success;
	// The URL of the following file can be computed from the Outbox URL.
	// The Outbox URL can be retrieved by invoking the TPPubWS.GetOutboxDocumentLibraries method that is defined
	// in the TPPubWS Web service. For additional information, see the BizTalk Server 2004 documentation.
	success = PutUtf8File(XDocument.DOM,"http://<servername:serverport>/sites/BASSite/Outbox/Form2.xml", false);
	eventObj.ReturnStatus = success;
}


//=======
// The method uses the WebDAV protocol to create a file at the specified URL.
// The code performs an HTTP PUT Web request to create an UTF-8 encoded XML file 
// at the specified location on the Windows SharePoint Services site.
// utf8XmlDoc - XML document that has the encoding attribute set to "UTF-8" or has no encoding attribute at all.
// fileUrl - The URL where the document will be created. It must include the file name.
// ovewrite - Set to value to true to overwrite the existing file or false to fail if a file that has the same URL exists.
//=======

function PutUtf8File(utf8XmlDoc, fileUrl, ovewrite) 
{
	// Create the xmlhttp object for transporting of the SOAP message.
	var xmlhttp = null;

	try
	{
		xmlhttp = new ActiveXObject("MSXML2.XMLHTTP.5.0");

		// Save the message as a UTF-8 encoded XML document.
		xmlhttp.open("PUT", fileUrl, false);
		xmlhttp.setRequestHeader("Content-Type", "text/xml; charset=utf-8");

		if (!ovewrite)
		{
			// Do not overwrite existing files.
			xmlhttp.setRequestHeader("If-None-Match", "*");
		}

		xmlhttp.send(utf8XmlDoc);
	}
	catch(ex)
	{
		var constServerErrorExc = -2146697208;
		if (ex.number != constServerErrorExc)
		{
			throw ex;
		}
	}

	// Examine the HTTP response.
	// Windows SharePoint Services returns 201 when a new file is created successfully
	// or returns 200 if the content of an existing file has been updated successfully.
	if ((xmlhttp.Status == 201) || (xmlhttp.Status == 200))
	{
		// Content has been saved successfully.
		return true;
	}
	else if (xmlhttp.Status == 412) // Precondition failed.
	{
		// File already exists.
		return false;
	}
	else
	{
		// An error was encountered.
		var ErrorMessage = xmlhttp.statusText;
		return false;
	}
}