I'm trying to user reflector installed on windows 7

On a corporate network. My PC appears in the mirroring icon on my iphone4s 6.1.3 but when I click on the name I don't get the option to mirror.

Same thing at home using same pc on home wifi.

My laptop "name" appears ok on the phone - so reflector seems to be running ok on the laptop.

Any ideas? Is there a magic setting on the iphone I'm missing?