My guess is that its failing to find the prompt you're asking it to find. Seems like the module is very specific as to how it finds those prompts so it can send commands. Take a look at the prompt you want the module to find and see if it has a ":" at the end or a new line (carrage return?) and then the ":" asking for the password.

I've never used Expect::Simple so I'm not sure if I'm right or not. It's a WAG at best. Hope it helps.