Your problem is a low-level connectivity problem:

500 Can't connect to 10.0.0.200:80 (connect: Operation now in progress
+)
[download]

Try setting $mech->timeout(0) and see if that fixes or changes the response. Also, make sure your web server is up and reachable - i.e. try wget or some other method to test it.

To really debug the problem I'd have a look at the output of strace perl yourscript.pl (assuming you are on a Unix-like box.) Then we'd see what the results of the connect() calls are. I'm sure this is coming from the second connect() attempt.

If you are on a Windows box then I have some other theories.