Long running System.Transactions (TransactionScope)

I've came accross a problem when working with long running System.Transactions (TransactionScope). An InvalidOperationException is thrown with the following message: "The transaction associated with the current connection has completed but has not been disposed. The transaction must be disposed before the connection can be used to execute SQL statements."

No transaction is reused, the usage of the connection and transaction is perfectly fine:

var transactionOptions = new TransactionOptions()
{
    IsolationLevel = IsolationLevel.Serializable,
    Timeout = TimeSpan.FromMinutes(20),
};
using (var connection = new SqlConnection(ConnectionString))
using (var transaction = new TransactionScope(TransactionScopeOption.Required, transactionOptions))
{
    // Some database manipulations that eventually throws the exception

    transaction.Complete();
}

The problem occurs if the transaction runs longer than the maxTimeout property. This property can only be modified in the machine.config and its default value is 10 minutes. It doesnt matter that the Timeout property of the TransactionOptions are set to a higher value, TransactionOptions.Timeout can not exceed maxTimeout property.

Your machine.config is located at: %windir%\Microsoft.NET\Framework\[version]\config\machine.config

On my current machine, they exist at (depending on target platform):

C:\Windows\Microsoft.NET\Framework\v4.0.30319\Config

C:\Windows\Microsoft.NET\Framework64\v4.0.30319\Config

To modify the machine.config add the following (in the configuration tag):

Be aware that the maxTimeout property is sometimes used for deadlock detection, so don't set a too high value.