How to fix Error 2278 on Windows Server 2025 / Windows 11

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Microsoft SQL Server 2025 Troubleshooting Guide: Error 2278

Why This Error Happens

Error 2278 (“A tag name may not start with the character ‘%c'”) occurs when SQL Server’s XML parser encounters malformed XML data, typically during FOR XML query execution, XML data type operations, or when processing XML-based configuration files such as SSIS packages. This is most often caused by invalid characters (such as numbers, symbols, or whitespace) appearing at the start of an XML element name, or by corrupted XML data being passed into a column, variable, or import file. It can also surface when application code dynamically generates XML tag names from user input or database values without proper sanitization, resulting in tags that violate XML naming rules.

Step-by-Step Resolution Guide

Step 1: Identify the Source of the Malformed XML

  • Check the SQL Server Error Log (C:\Program Files\Microsoft SQL Server\MSSQL17.MSSQLSERVER\MSSQL\Log\ERRORLOG) for the exact query or procedure that triggered the error.
  • Run SELECT * FROM sys.dm_exec_requests WHERE session_id = @@SPID to capture the offending query text if the session is still active.
  • Review any FOR XML PATH or FOR XML AUTO queries where column names or aliases are being used directly as XML tag names.

Step 2: Sanitize Column Names and Aliases Used as XML Tags

  • Ensure all column aliases used in FOR XML PATH('TagName') start with a letter or underscore, never a digit or special character (e.g., change FOR XML PATH('1Item') to FOR XML PATH('Item1')).
  • If tag names are generated dynamically from table data, add a validation step using PATINDEX('[^a-zA-Z_]%', @TagName) to catch invalid leading characters before building the XML.
  • Replace or strip invalid characters using REPLACE() or TRANSLATE() functions in T-SQL prior to XML construction.

Step 3: Validate and Repair Source XML Files or Columns

  • If importing XML via OPENROWSET(BULK...) or xml data type columns, open the source file in a text editor and confirm no tag starts with a number, hyphen, or whitespace.
  • Use SELECT CAST(xmlcolumn AS XML) in a test query to isolate which row contains the invalid XML before bulk processing.
  • For SSIS packages, open the .dtsx file in XML/text mode and check custom-generated nodes for naming violations.

Step 4: Apply SQL Server 2025 Cumulative Update if Parser-Related

  • Navigate to Microsoft’s official download center and install the latest Cumulative Update (CU) for SQL Server 2025, as early builds had known XML parser edge-case bugs.
  • Restart the SQL Server service via services.msc or Restart-Service MSSQLSERVER in PowerShell after patching.

Alternative or Verification Steps

  • Re-run the original query or import job and confirm it completes without Error 2278, then spot-check the output XML in SSMS’s XML viewer to confirm proper tag structure.
  • If the error persists, isolate the exact row/record using a binary search approach (processing data in smaller batches) to pinpoint the specific malformed entry, then correct it at the data source rather than at the query level.