How to fix Error 6323 on Windows Server 2025 / Windows 11

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Troubleshooting Guide: SQL Server Error 6323 — XML Schema Collection Altered During Batch Execution

Why This Error Happens

This error occurs when a Transact-SQL batch references an XML schema collection that is modified (via ALTER XML SCHEMA COLLECTION or DROP) by a DDL statement within the same batch before the variable using it is processed. SQL Server 2025 compiles and validates XML-typed variables against the schema collection at the start of batch execution, so any mid-batch alteration invalidates that binding. This typically results from poorly structured scripts, migration tools, or ORM-generated batches that combine schema DDL and XML variable declarations/usage in a single GO-less execution unit.

Step-by-Step Resolution Guide

Step 1: Identify the Conflicting Batch Structure

  • Open the failing script in SQL Server Management Studio (SSMS) connected to your SQL Server 2025 instance.
  • Locate any CREATE XML SCHEMA COLLECTION, ALTER XML SCHEMA COLLECTION, or DROP XML SCHEMA COLLECTION statements.
  • Check whether these DDL statements exist in the same batch as variable declarations of type XML (schema_collection_name).

Step 2: Separate DDL Operations Using Batch Terminators

  • Insert a GO statement immediately after any XML schema collection DDL operation.
  • Ensure the XML variable usage occurs in a separate batch, for example:
  ALTER XML SCHEMA COLLECTION dbo.MySchemaCollection ADD '<schema .../>';
  GO
  DECLARE @x XML (dbo.MySchemaCollection);
  SET @x = '<root/>';
  GO
  • Save the script and re-run it through SSMS or sqlcmd to confirm batch isolation.

Step 3: Update Deployment and Migration Scripts

  • If the batch originates from an automated deployment tool (e.g., DACPAC, Flyway, or a custom PowerShell deployment script), locate the template that generates combined DDL/DML batches.
  • Modify the script generator to insert explicit GO separators after every XML schema collection modification statement.
  • Redeploy using sqlcmd -S <ServerName> -i deploy.sql on Windows Server 2025 to validate the corrected batch sequencing.

Step 4: Check for Application-Level Batching Issues

  • If the error originates from an application (e.g., .NET using SqlCommand.ExecuteNonQuery), verify that multiple SQL statements combined into a single command text do not mix schema DDL and XML variable operations.
  • Split the command into two sequential SqlCommand executions, ensuring the schema alteration commits before the XML variable batch runs.

Alternative or Verification Steps

  • Re-run the corrected script in SSMS and confirm no Error 6323 appears in the Messages tab; check Event Viewer > Applications and Services Logs > MSSQLSERVER for confirmation that no related errors were logged.
  • If the issue persists, use sp_help 'dbo.MySchemaCollection' to confirm the schema collection is in a stable, non-altered state, and verify no concurrent sessions are modifying the same schema collection using sys.dm_exec_requests.