getJSON get wrong content but no error returned

getJSON get wrong content but no error returned


for picasa, if enter a wrong userid in the link, the page will print a
string "Unable to find user with email xxx@gmail.com" instead of a
json object.
Is there anyway to detect the return string is in wrong format?
I tried ajaxComplete,ajaxError,ajaxStop,ajaxSuccess, none of them
triggered if the remote file is in wrong format.
And if I put a button in the page to trigger ajax, the first time
ajaxSend is triggered, but from the second time ajaxSend not working.
I am using jquery-1.3.1.min.js.
Appreciate any reply.