Which version of WWW::Mechanize/LWP...? It pays to always have the latest installed

Anyone seen something like this before and/or can explain what's going on ?

Simple answer for all such questions (whats going on), is that webservers can be as crazy/dumb as they want

For example, webserver set a counter in a cookie ... which after 194 requests has a value the webserver doesn't know how to handle, so it quits (bad request)