C＃不能隐式地将类型T转换为类型T.

my method:

public TableFilled<TKey, TRow> getTera()
    {

        Func<TablesFilled<TKey,TRow>> _getTera=new Func<TablesFilled<TKey,TRow>>(
        ()=>{return (TablesFilled<TKey,TRow>) chGetTera();});

       //Above does not compile says: Cannot convert type 
       //'AcapsVerify.FunctionalTables.TableFilled<TKey,TRow>' to 
       //'AcapsVerify.FunctionalTables.TablesFilled<TKey,TRow>'
       // the line below has the same blue underline error.
       return _getTera.TimeAndReport("Finished Teradata",OutputIfListener);

       // this works fine
       return chGetTera;
    }
public TableFilled<TKey, TRow> get