How to fix Error 7899 on Windows Server 2025 / Windows 11

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Troubleshooting Guide: Error 7899 – SOAP Unsupported Data Type in SQL Server 2025

Why This Error Happens

This error occurs because SQL Server’s native SOAP/HTTP endpoint feature only recognizes a legacy set of data types that were valid in SQL Server 2005 and earlier, such as sql_variant, xml (in certain contexts), newer large-value types, or CLR user-defined types which fall outside this supported list. When a stored procedure or function exposed through a SOAP endpoint attempts to return a modern or unsupported data type, the SOAP serialization layer fails and throws Error 7899. This is fundamentally a legacy-compatibility limitation rather than a permissions or connectivity issue, since Microsoft deprecated native XML Web Services (SOAP endpoints) starting with SQL Server 2008, and they exist in SQL Server 2025 only for backward compatibility.

Step-by-Step Resolution Guide

Step 1: Identify the Offending Stored Procedure or Function

  • Review the SOAP endpoint definition using sys.endpoints and sys.endpoint_webmethods to list exposed procedures.
  • Run sp_helptext '<procedure_name>' to inspect the return type of the procedure or function tied to the endpoint.
  • Look specifically for return types like sql_variant, hierarchyid, geography, geometry, datetime2, datetimeoffset, time, xml, nvarchar(max), varbinary(max), or CLR-based types.

Step 2: Modify the Procedure to Use a Legacy-Compatible Data Type

  • Alter the stored procedure to cast or convert the return value into a supported type, such as int, varchar, nvarchar, datetime, decimal, or float.
  • Example fix:
ALTER PROCEDURE dbo.GetOrderStatus
AS
BEGIN
    SELECT CAST(OrderStatusDateTime AS datetime) AS OrderStatus
    FROM dbo.Orders
END
  • Avoid using datetime2 or datetimeoffset in any procedure mapped to a SOAP WEBMETHOD.

Step 3: Recreate or Refresh the SOAP Endpoint

  • Drop and recreate the HTTP endpoint to ensure metadata is refreshed after altering the procedure:
DROP ENDPOINT MySoapEndpoint;
GO
CREATE ENDPOINT MySoapEndpoint
STATE = STARTED
AS HTTP (
    PATH = '/sql/soap',
    AUTHENTICATION = (INTEGRATED),
    PORTS = (CLEAR)
)
FOR SOAP (
    WEBMETHOD 'GetOrderStatus' (NAME='AdventureWorks.dbo.GetOrderStatus'),
    WSDL = DEFAULT
);
  • Confirm the endpoint state is STARTED using SELECT name, state_desc FROM sys.endpoints;.

Step 4: Migrate Away from SOAP Endpoints (Recommended Long-Term Fix)

  • Since native SOAP endpoints are deprecated and unsupported for modern workloads, redesign the integration using a REST API layer (e.g., via ASP.NET Core Web API, Azure Functions, or SQL Server’s native JSON support) that queries SQL Server directly.
  • Export existing WSDL consumers to a transitional web service wrapper that internally calls SQL Server using ADO.NET or ODBC, bypassing native SOAP entirely.

Alternative or Verification Steps

  • To verify the fix, invoke the WEBMETHOD again through a SOAP client (e.g., SoapUI) or browse to http://<server>/sql/soap?wsdl and confirm the WSDL generates without errors, then execute the method to confirm a valid XML response is returned.
  • If modifying the data type is not feasible due to application dependencies, consider wrapping the original procedure in a new procedure that explicitly converts the final output into varchar or nvarchar before returning results through the SOAP endpoint.