Entity Framework: There is already an open DataReader associated with this Command

When using Entity Framework I sometimes got the following error:

EntityCommandExecutionException

{"There is already an open DataReader associated with this Command which must be closed first."}
   at System.Data.EntityClient.EntityCommandDefinition.ExecuteStoreCommands...

The solution I found involved converting the IQueriable collection into other enumerable collection e.g.

_dbContext.Users.ToList()