Ok, I think i got the problem where it is, looks like you're URLEncoding the while Basestring. it shouldn't be
GET&(URLEncode(URI))&(Normalizedparams).
Normalizedparams=UrlEncode(oauth_consumer_key)&UrlEncode(oauth_nonce)&.....so on
You should be able to nail it this time:)
Thanks,
-Rajiv