hi ..,
i think you are not passing the correct encoding string to the method
FromBase64String
here am explaining with an example...
let say the original string is
rajesh
if you encode it using base64 you will get
cmFqZXNoDQo=
if decode the encoded sting you will get original string like this ....
<pre lang="vb">? Convert.FromBase64String("cmFqZXNoDQo=")
{byte[8]}
[0]: 114
[1]: 97
[2]: 106
[3]: 101
[4]: 115
[5]: 104
[6]: 13
[7]: 10
Thanks
Rajesh B