How to fix Error 2310 on Windows Server 2025 / Windows 11

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Troubleshooting Guide: SQL Server Error 2310 – “The attribute ‘%ls’ is declared more than once”

Why This Error Happens

This error occurs when SQL Server 2025 parses an XML Schema Collection, XML document, or SSIS/DACPAC metadata file (such as a .dacpac, .bacpac, or XSD-based schema) that contains a duplicate attribute definition within the same element or complex type. This is typically caused by a corrupted or manually edited XML/schema file, a flawed schema merge during an upgrade from a previous SQL Server version, or a third-party tool generating malformed XML with redundant attribute declarations. Because the XML parser enforces strict uniqueness constraints on attribute names within a given scope, it rejects the entire schema or document load, halting the associated operation (e.g., CREATE XML SCHEMA COLLECTION, SSDT deployment, or Service Broker message validation).

Step-by-Step Resolution Guide

Step 1: Identify the Offending XML Source

  • Check the SQL Server Error Log at C:\Program Files\Microsoft SQL Server\MSSQL17.MSSQLSERVER\MSSQL\Log\ERRORLOG for the full error context, including the schema collection name or file path.
  • If triggered by a deployment, inspect the .dacpac/.bacpac file by renaming it to .zip and extracting it to review model.xml for duplicate attributes (e.g., search for repeated Name= entries within the same <Element> tag).
  • Run the following to identify the schema collection in question:
  SELECT name, xml_schema_namespace FROM sys.xml_schema_collections;

Step 2: Correct the Duplicate Attribute in the Source File

  • Open the identified XML/XSD file in a validating editor (Visual Studio 2025 or VS Code with the XML extension installed).
  • Locate the element flagged in the error message and remove or rename the duplicate attribute so each attribute name appears only once per element scope.
  • Save the file with UTF-8 encoding to avoid introducing hidden byte-order-mark (BOM) corruption that can also trigger parser errors.

Step 3: Re-register or Re-import the Corrected Schema

  • If the error originates from a schema collection, drop and recreate it:
  DROP XML SCHEMA COLLECTION dbo.MySchemaCollection;
  GO
  CREATE XML SCHEMA COLLECTION dbo.MySchemaCollection AS N'<corrected XML content>';
  GO
  • For DACPAC/BACPAC deployments, re-zip the corrected model.xml back into the package and redeploy using SqlPackage.exe from an elevated PowerShell prompt on Windows Server 2025.
  • Clear any cached deployment artifacts in %TEMP%\SqlPackageTemp before retrying.

Step 4: Validate Upstream Tooling

  • If the file was auto-generated (e.g., via SSDT, SSIS, or a CI/CD pipeline), update the generating tool to the latest version, as older versions are known to emit duplicate attribute nodes during schema merges.
  • Re-run the generation process and re-diff the output XML against the previous corrupted version.

Alternative or Verification Steps

  • Validate the fix by re-running the original failing command (schema creation, deployment, or Service Broker message send) and confirming Error 2310 no longer appears in the Error Log or SSMS output pane.
  • As an alternative, use an XSD validation tool (e.g., xmllint --noout --schema or Visual Studio’s “Validate XML” feature) against the corrected file before reloading it into SQL Server to catch any remaining structural issues proactively.