How to fix Error 2755 on Windows Server 2025 / Windows 11

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Troubleshooting Guide: Error 2755 – Invalid SET DEADLOCK_PRIORITY Option

Why This Error Happens

This error occurs when the SET DEADLOCK_PRIORITY statement is passed a value that does not match the parser’s accepted syntax, which is strictly limited to the keywords HIGH, NORMAL, LOW, or an integer literal between -10 and 10. In most cases, this is triggered by application code or legacy scripts sending a string, a variable of the wrong data type, or an out-of-range integer directly to the session option. Occasionally this surfaces after migrating databases to SQL Server 2025, where stricter T-SQL parsing rules expose syntax that older engine versions silently tolerated.

Step-by-Step Resolution Guide

Step 1: Locate the Offending T-SQL Statement

  • Check the SQL Server error log or Extended Events session for the exact query text that triggered Error 2755.
  • Look specifically for lines containing SET DEADLOCK_PRIORITY in stored procedures, triggers, or application connection strings.
  • Use sys.dm_exec_sql_text combined with a recent query hash if the session has already disconnected.

Step 2: Correct the Syntax to a Valid Value

  • Replace any invalid keyword or string with one of the accepted literals: HIGH, NORMAL, or LOW.
  • If using a numeric value, ensure it falls strictly within the range of -10 to 10 (e.g., SET DEADLOCK_PRIORITY 5;).
  • Remove any quotation marks around the keyword, since SET DEADLOCK_PRIORITY 'HIGH' is invalid — it must be SET DEADLOCK_PRIORITY HIGH;.

Step 3: Audit Application and ORM-Generated Code

  • Search connection pooling or ORM frameworks (Entity Framework, Hibernate, Dapper) for dynamically injected session settings.
  • Confirm that no configuration file or environment variable is passing a non-integer string (like "VeryHigh") into the deadlock priority parameter.
  • Update any stored procedure parameters so the data type matches smallint or a validated string constrained to the three keywords.

Step 4: Test in Isolation Using SSMS

  • Open a new query window in SQL Server Management Studio connected to the Windows Server 2025 instance.
  • Run the corrected statement alone, e.g.:
  SET DEADLOCK_PRIORITY LOW;
  • Confirm no error is returned before reintegrating the fix into the full script or application.

Alternative or Verification Steps

  • Re-run the original transaction or stored procedure that failed and confirm Error 2755 no longer appears in the SQL Server error log or client application output.
  • If the error persists, check for mixed-mode scripts where DEADLOCK_PRIORITY is set via a dynamically built SQL string (EXEC(@sql)) — concatenation errors here often reintroduce invalid values even after direct code fixes.