"This SqlTransaction has completed; it is no longer usable."... configuration error?

I believe this error message is due to a "zombie transaction".

Look for possible areas where the transacton is being committed twice (or rolled back twice, or rolled back and committed, etc.). Does the .Net code commit the transaction after the SP has already committed it? Does the .Net code roll it back on encountering an error, then attempt to roll it back again in a catch (or finally) clause?

It's possible an error condition was never being hit on the old server, and thus the faulty "double rollback" code was never hit. Maybe now you have a situation where there is some configuration error on the new server, and now the faulty code is getting hit via exception handling.

Can you debug into the error code? Do you have a stack trace?

I had this recently after refactoring in a new connection manager. A new routine accepted a transaction so it could be run as part of a batch, problem was with a using block:

public IEnumerable<T> Query<T>(IDbTransaction transaction, string command, dynamic param = null)
{
  using (transaction.Connection)
  {
    using (transaction)
    {
      return transaction.Connection.Query<T>(command, new DynamicParameters(param), transaction, commandType: CommandType.StoredProcedure);
    }
  }
}

It looks as though the outer using was closing the underlying connection thus any attempts to commit or rollback the transaction threw up the message "This SqlTransaction has completed; it is no longer usable."

I removed the usings added a covering test and the problem went away.

public IEnumerable<T> Query<T>(IDbTransaction transaction, string command, dynamic param = null)
{
  return transaction.Connection.Query<T>(command, new DynamicParameters(param), transaction, commandType: CommandType.StoredProcedure);
}

Check for anything that might be closing the connection while inside the context of a transaction.

Had the exact same problem and just could not find the right solution. Hope this helps somebody.

I have an .NET Core 3.1 WebApi with EF Core. Upon receiving multiple calls at the same time, the applications was trying to add and save changes to the database at the same time.

In my case the problem was that the table that the data would be saved in, did not have a primary key set.

Somehow EF Core missed when the migration was ran from the application that the ID in the model was supposed to be a primary key.

I found the problem by opening the SQL Profiler and seeing that all transactions was successfully submitted to the database (from the application) but only one new row was created. The profiler also showed that some type of deadlock was happening but I couldn't see much more in the trace logs of the profiler. On further inspection I noticed that the primary key identifier was missing on the column "Id".

The exceptions I got from my application was:

This SqlTransaction has completed; it is no longer usable.

and/or

An exception has been raised that is likely due to a transient failure. Consider enabling transient error resiliency by adding 'EnableRetryOnFailure()' to the 'UseSqlServer' call.

I have the same problem. This error occurs because conection pooling. When exists two or more users acess the system the connetion pooling reuse a connetion and the transation too. If the first user execute commit ou rollback the transaction is no longe usable.