Question: Imagine an abstract problem. 

There is a client (`C`) that interacts to a server(`S`). They changes a date variable(`d`).

A server can be French or English, the client too. 

A date sent by a French client ("31/12/2011") to an English Server("12/31/2011") can't recognize it. And viceversa. 

How to avoid such a problem in .NET.

Answer: 
Send it between the client and server using the Ticks property. That's a number and will always be the same no matter what you want to format the date as.
Is there any reason why you are sending the date as string? The best thing would be to share the date using DateTime datatype. If for any reason, you can just send the string, best is to convert the date value to LongDateFormat and then transfer, which could be parsed on the other end to get the meaningful date.