Exception "developer token in invalid"

[Digitally_Yours]

i have downloaded the sample code to use Google api in .net.
and followed these http://code.google.com/apis/adwords/docs/developer/adwords_api_sandbox.html
Instruction to test .
Now i am getting an exception whenever i make call to web service .
Exception is "The developer token in invalid".
I am sending requst to sandbox and using my gmail email address.
my adword login info is :
private static String email = "digitall...@gmail.com";
private static String password = "*******";
private static String clientEmail = "";
private static String useragent = "abcds";
private static String developerToken =
"digitall...@gmail.com++USD";
private static String applicationToken ="";
im using the adword api for the first time .
Plz help me.
regards
Ishtiaq ahmed