In my scenario, the exception was being thrown because I was trying to create a new connection instance within a TransactionScope on an already existing connection:
Example:
void someFunction()
{
using (var db = new DBContext(GetConnectionString()))
{
using (var transaction = new TransactionScope(TransactionScopeOption.Required, new TransactionOptions { IsolationLevel = System.Transactions.IsolationLevel.ReadUncommitted }))
{
someOtherFunction(); // This function opens a new connection within this transaction, causing the exception.
}
}
}
void someOtherFunction()
{
using (var db = new DBContext(GetConnectionString()))
{
db.Whatever // <- Exception.
}
}