字符串。十进制值的格式阻塞?

我希望下面的两个测试(为NUnit编写)都能通过,但是十进制版本失败,出现“System.FormatException:Format说明符无效”和双精度版本一样。我不明白为什么。有人能帮我亮灯吗?

谢谢;

[Test]
public void Integer_Format_Hex()
{
    //Assume
    Int32 myValue = 11101110;

    //Arrange

    //Act

    //Assert
    Assert.That( String.Format( "0x{0:X8}" , myValue ) , Is.EqualTo( "0x00A963B6" ) );
}

[Test]
public void Decimal_Format_Hex()
{
    //Assume
    Decimal myValue = 11101110m;

    //Arrange

    //Act

    //Assert
    Assert.That( String.Format( "0x{0:X8}" , myValue ) , Is.EqualTo( "0x00A963B6" ) );
}

[Test]
public void Decimal_Format_Hex2()
{
    //Assume
    Decimal myValue = 11101110m;

    //Arrange

    //Act

    //Assert
    Assert.That( myValue.ToString( "X" ) , Is.EqualTo( "00A963B6" ) );
}