How To Avoid ASP.NET SqlServer Session To Interfer With The Ambient Transaction-Per-Request?

I am trying to use a transaction scope in a transaction-per-request pattern. So I have a http module that do (simplified):

private void Application_BeginRequest(object sender, EventArgs e)
{
var scope = new TransactionScope(TransactionScopeOption.RequiresNew);
PutScopeInHttpContext(scope);
}

private void Application_EndRequest(object sender, EventArgs e)
{
var scope = GetScopeFromHttpContext();
try
{
if (HttpContext.Current.Error == null)
{
scope.Complete();
}
}
finally
{
scope.Dispose();
}
}


Then, in my web.config, I have:

<httpModules>
<clear/>
<add name="OutputCache" type="System.Web.Caching.OutputCacheModule"/>
<add name="Session" type="System.Web.SessionState.SessionStateModule"/>
<add name="Profile" type="System.Web.Profile.ProfileModule"/>
<add name="ScriptModule" type="System.Web.Handlers.ScriptModule, System.Web.Extensions, Version=3.5.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35"/>
<add name="UrlRoutingModule" type="System.Web.Routing.UrlRoutingModule, System.Web.Routing, Version=3.5.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35"/>
<add name="TransactionPerRequestWebModule" type="Acme.Web.TransactionPerRequestWebModule, Acme.Web"/>
</httpModules>
<sessionState mode="SQLServer" sqlConnectionString="Data Source=localhostSQLEXPRESS;Integrated Security=SSPI;" cookieless="false" timeout="360"/>


Now, at what seem like randomly rate, roughly 1 page out of ten gives me the following error:

[SqlException (0x80131904): Distributed transaction completed. Either enlist this session in a new transaction or the NULL transaction.]
System.Data.SqlClient.SqlConnection.OnError(SqlException exception, Boolean breakConnection) +1951450
System.Data.SqlClient.SqlInternalConnection.OnError(SqlException exception, Boolean breakConnection) +4849003
System.Data.SqlClient.TdsParser.ThrowExceptionAndWarning(TdsParserStateObject stateObj) +194
System.Data.SqlClient.TdsParser.Run(RunBehavior runBehavior, SqlCommand cmdHandler, SqlDataReader dataStream, BulkCopySimpleResultSet bulkCopyHandler, TdsParserStateObject stateObj) +2394
System.Data.SqlClient.SqlDataReader.ConsumeMetaData() +33
System.Data.SqlClient.SqlDataReader.get_MetaData() +83
System.Data.SqlClient.SqlCommand.FinishExecuteReader(SqlDataReader ds, RunBehavior runBehavior, String resetOptionsString) +297
System.Data.SqlClient.SqlCommand.RunExecuteReaderTds(CommandBehavior cmdBehavior, RunBehavior runBehavior, Boolean returnStream, Boolean async) +954
System.Data.SqlClient.SqlCommand.RunExecuteReader(CommandBehavior cmdBehavior, RunBehavior runBehavior, Boolean returnStream, String method, DbAsyncResult result) +162
System.Data.SqlClient.SqlCommand.RunExecuteReader(CommandBehavior cmdBehavior, RunBehavior runBehavior, Boolean returnStream, String method) +32
System.Data.SqlClient.SqlCommand.ExecuteReader(CommandBehavior behavior, String method) +141
System.Data.SqlClient.SqlCommand.ExecuteReader() +89
System.Web.SessionState.SqlSessionStateStore.DoGet(HttpContext context, String id, Boolean getExclusive, Boolean& locked, TimeSpan& lockAge, Object& lockId, SessionStateActions& actionFlags) +516

[HttpException (0x80004005): Unable to connect to SQL Server session database.]
System.Web.SessionState.SqlSessionStateStore.ThrowSqlConnectionException(SqlConnection conn, Exception e) +229
System.Web.SessionState.SqlSessionStateStore.DoGet(HttpContext context, String id, Boolean getExclusive, Boolean& locked, TimeSpan& lockAge, Object& lockId, SessionStateActions& actionFlags) +649
System.Web.SessionState.SqlSessionStateStore.GetItemExclusive(HttpContext context, String id, Boolean& locked, TimeSpan& lockAge, Object& lockId, SessionStateActions& actionFlags) +48
System.Web.SessionState.SessionStateModule.GetSessionStateItem() +117
System.Web.SessionState.SessionStateModule.BeginAcquireState(Object source, EventArgs e, AsyncCallback cb, Object extraData) +487
System.Web.AsyncEventExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute() +66
System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously) +155


What I (think I) understand is that the connection to the ASP.NET session database is sometimes enlisted in my business transaction, and I get this error when my business transaction is completing first.

There is a couple of problem with that:


I don't think the transaction for the session state should be the same as my business one. These are 2 separate concerns.
It makes the transaction automatically escalate to a distributed (MSDTC) one, which impacts my performance.

How do I decouple my business transaction from the ASP.NET session one?