Actually I did follow Zach Graves's instruction on getting the access token and secret in the Flash SDK
http://developer.yahoo.net/forum/index.php?showtopic=387

And then try using the API to do YQL:

var user:YahooUser = session.getSessionedUser();
user.yql.addEventListener(YahooResultEvent.YQL_QUERY_SUCCESS, handleYQLSuccess);
user.yql.query("select * from social.profile where guid=me");

However, I still face the error saying:
Error opening URL 'http://query.yahooapis.com/v1/yql?format=json&oauth_signature_method=HMAC-SHA1&oauth_consumer_key=dj0yJmk9RG1MTlhBYk9FZVBPJmQ9WVdrOVExRTBVVEUzTlRnbWNHbzlNa
kV6TmpJNU5qVTBOUS0tJnM9Y29uc3VtZXJzZWNyZXQmeD0zOA--&oauth_timestamp=1228876134&region=US&oauth_version=1.0&oauth_token=A=6_pU_vL6kAdVxRAzVoI3Jk4y1kfar9cd0_m0Kzj2S2d61njkx_BAccgudP6sfP
TPxXYpqWlVfxmD6RjSKbZuYXjCH.8F9QgGGd2UBUb2NmsF6IVcRkgm0qqnzYH8wggu11JFSnoAFhmCOD
w
GXMlsI7K_7JYDaf8nvm0Z2s1jleqUXxgq1dT.b5siCMeCohoiHj5xz4jlpsKWymGafmyBjqnjhrTHgmt
n
CzHMIlj4rJTl04Pb3K.6_1B2.r7DOMl8ZFwyesh9Iaz7XjP7CoQE2t7lYSgCzVd_0pjEBfKD1Z8w3M8i
l
eBWMqBa4EmQmTqLkOmAIpE7mZLOqi_h81eQHMSFsiEATdzvyqUpBn1TU1bof_9aHpGG8ZoKhUCUI7bM4
6
hiMt3pzkQlOJBfSmz7PqH8cKtkBjYxygjKMEM5ew2.3xIf8n_z4itDgD44I2WIQh_twv7g3790iNWSIi
T
TkzIRnl83JqTU6gmbV.bj1l.JIZLGdrX8o1HrzNz3zPDHjbZ8NNUYobDW.OM4JRTvawPGuv2t_27g59K
v
DWhR1rOSXmqh8w3I1CndEBbYN9K69bdoHBr1IY4aGnQdUTvrNIORVrBp1aPGYtYEA0NQcDQqn3OtOgcF
a
SB8Np0oemHTj48j3FKPFeNxpBMiKsLRmczXwGe0Y7s9sB1KjgmVQOE0J12IeOCXv9s9h.5eehkWJvy98
.
kUyOMCg0w_FXDQ7gzTh32Zjw--&lang=en-US&q=select%20%2A%20from%20social.connections%20where%20owner_guid%3Dme&oauth_signature=vp6soD0CrUIXhVZtzarUUsPOFVs=&oauth_nonce=843810e585812fb537df681d33c0a5e2'

Please see this topic: http://developer.yahoo.net/forum/index.php?showtopic=494