Well, the issue is likely related to either cookies, or to the http_referer string....

your error:
Sorry, we're unable to process this request. There are two possible causes for this error:

You accessed this page via a bookmark instead of entering through the AdWords Select homepage
this one is probably because there is no http_referer set in the LWP au

You have disabled cookies in your browser.

this one is because the jsession id has changed

The answer to these is probably to use LWP to get the page first, ie, establish a session... and then after that, return the form (jsession included) as it was presented.

good luck!