SQL related error in event viewer any ideas? this happend all of sudden.

Type: System.InvalidOperationException
Message: SqlConnection does not support parallel transactions.
StackTrace:
at System.Data.SqlClient.SqlInternalConnection.BeginSqlTransaction(IsolationLevel iso, String transactionName, Boolean shouldReconnect)
at System.Data.SqlClient.SqlConnection.BeginTransaction(IsolationLevel iso, String transactionName)
at Microsoft.Dynamics.Nav.Runtime.NavSqlConnection.ExecuteFunction[T](Func`1 function, NavSqlCommand command)
at Microsoft.Dynamics.Nav.Runtime.NavSqlConnection.ExecuteFunctionWithTrace[T](EventTask task, Func`1 function, NavSqlCommand command)
at Microsoft.Dynamics.Nav.Runtime.NavSqlConnection.BeginTransaction(IsolationLevel newIsolationLevel)
at Microsoft.Dynamics.Nav.Runtime.NavSqlConnection.CheckBeginTransaction(TransactionType transactionType)
at...