Error proof way to convert an enum value into a custom string in C#

Here is a code snippet I ran into the other day:

string strMsgType = "";
switch (messageType)
{
case MessageTypes.GeneralMessage:
strMsgType = "0";
break;
case MessageTypes.TargetMessage1On1:
strMsgType = "1";
break;
case MessageTypes.GroupMessage:
strMsgType = "2";
break;
case MessageTypes.BroadcastMessage:
strMsgType = "3";
break;
case MessageTypes.CallBackMessage:
strMsgType = "4";
break;
case MessageTypes.NoticeMessage:
strMsgType = "5";
break;
case MessageTypes.PaperMessage:
strMsgType = "6";
break;
case MessageTypes.DigitalMessage:
strMsgType = "8";
break;
case MessageTypes.LimitedMessage:
strMsgType = "9";
break;
case MessageTypes.SaleMessage:
strMsgType = "A";
break;
case MessageTypes.AdMessage:
strMsgType = "B";
break;
case MessageTypes.RadioAdMessage:
strMsgType = "C";
break;
case MessageTypes.TvAdMessage:
strMsgType = "D";
break;
case MessageTypes.OtherMessage:
strMsgType = "E";
break;
}

It corresponds to the following enum:

public enum MessageType
{
GeneralMessage = 0,
TargetMessage1On1 = 1,
GroupMessage,
BroadcastMessage,
CallBackMessage,
NoticeMessage,
PaperMessage,
DigitalMessage,
LimitedMessage,
SaleMessage,
AdMessage,
RadioAdMessage,
TvAdMessage,
OtherMessage
}

As you can see, there is a bug in the code as it did not have a case statement for enum value 7. It turns out that, that was as designed, i.e. there should never be an enum value 7, which means the enum declaration is incorrect. Either way, there is a bug in the above code.

It is not uncommon to have specific literal values for the enum strings and trying to correlate those literal values with a switch statement elsewhere is tedious and could be bug prone. Instead a better way to convert an enum value to a custom string would be to do something like this:

string s = Convert.ToInt32(messageType).ToString("X0");

I would love to hear what you think?