Question: I am working on CRC64 Reversing algorithm on C# but unable to code it. If anyone can help me out, it will be nice of him. I am desperate to complete the coding.

Answer: 
That's not possible. CRC is a [hash function](http://en.wikipedia.org/wiki/Hash_function). Hash functions **cannot** be reversed. The best you can do is try and find collisions for a given hash, but they are *designed* to be hard to find such collisions..
You definitely won't be able to reverse it, since you lose critical data doing the "forward" computation that would be necessary to the "backward" computation. You can try to brute-force it if you have some idea of what the input might have been, but because a CRC is weak there might be a lot of collisions (meaning you might find lots of possible inputs that could have generated your result) in which case you have no way of knowing which one is correct.