Troubleshooting Guide: SQL Server Error 7875 – Unexpected XML Construct in SOAP Request

Why This Error Happens

This error occurs when SQL Server’s Native XML Web Services (SOAP endpoint listener) receives a SOAP request where the character data inside a specific XML element contains invalid or malformed content, such as embedded markup, improperly escaped characters, or mixed content that violates the XML Schema Definition (XSD) bound to that namespace. This typically happens due to a mismatch between the client-side SOAP serializer and the WSDL contract generated by SQL Server, or because the request payload was corrupted/truncated during transit. It can also occur if a custom application is manually constructing XML payloads and fails to properly encode special characters (like &, <, >) before transmission.

Step-by-Step Resolution Guide

Step 1: Validate the Raw SOAP Payload

• Capture the raw SOAP request using a network trace tool (e.g., Fiddler, Wireshark, or SQL Server Profiler with “SOAP” event filters enabled).
• Inspect the specific element named in the error message (replace %.*ls with the actual element/namespace reported in the SQL Server error log).
• Check for unescaped special characters (&, <, >, ', ") inside the character data that should have been XML-encoded by the client.

Step 2: Verify the WSDL and Endpoint Schema Binding

• Open a command prompt and query the endpoint metadata directly:

  sqlcmd -S YourServerName -Q "SELECT * FROM sys.http_endpoints"

• Confirm the IS_XML_SCHEMA_STRICT setting hasn’t drifted from the client’s expected schema version.
• Re-generate the WSDL reference on the client side by navigating to https://YourServer/sql/endpoint?wsdl and refreshing the proxy class to ensure the client and server contracts match.

Step 3: Repair or Rebuild the SOAP Endpoint

• On the SQL Server instance, drop and recreate the affected endpoint using T-SQL:

  DROP ENDPOINT YourSoapEndpoint;
  GO
  CREATE ENDPOINT YourSoapEndpoint
      STATE = STARTED
      AS HTTP (
          PATH = '/sql/endpoint',
          AUTHENTICATION = (INTEGRATED),
          PORTS = (SSL)
      )
      FOR SOAP (
          WEBMETHOD 'YourMethod' (NAME = 'YourDB.dbo.YourProc'),
          WSDL = DEFAULT,
          SCHEMA = STANDARD
      );
  GO

• Restart the SQL Server service via services.msc or net stop MSSQLSERVER && net start MSSQLSERVER to flush any cached endpoint metadata.

Step 4: Patch Client-Side Encoding Logic

• If using a .NET or Java client, ensure the XML writer is using XmlWriter.Create() with default encoding settings rather than manual string concatenation for building SOAP envelopes.
• Apply System.Security.SecurityElement.Escape() (or equivalent) to any user-supplied text fields before inserting them into the XML body.

Alternative or Verification Steps

• Re-send a known-good SOAP test request (using a tool like SoapUI) against the endpoint to confirm the server now processes the payload without throwing Error 7875.
• If the error persists, bypass Native XML Web Services entirely by migrating the integration to a modern REST/JSON endpoint via SQL Server’s HTTP API layer, since SOAP-based endpoints are considered a legacy compatibility feature and are more prone to strict schema violations.