Thanks for your help. Your code is working and I finally find out the reason 
My .NET code generate nonce like this:
In Python code, it generate nonce like this:
In like case, as it always smaller than the last .NET nonce in one account, then MtGox regards it as invalid and can't get authorization.
I simply added more zero to "int(time.time()*1000000000)" and it then works.
(or If I using one account for Python only, then it have no such problem also.)
Again, thanks for your code
My .NET code generate nonce like this:
Code:
string parameters = "nonce=" + DateTime.Now.Ticks.ToString();
it'll generate a 18 length value like 634705522019762907In Python code, it generate nonce like this:
Code:
string parameters = "nonce=" + DateTime.Now.Ticks.ToString();
which will generate 16 length value like 133492738213800In like case, as it always smaller than the last .NET nonce in one account, then MtGox regards it as invalid and can't get authorization.
I simply added more zero to "int(time.time()*1000000000)" and it then works.
(or If I using one account for Python only, then it have no such problem also.)
Again, thanks for your code