Currently, the installer and activation client cannot browse to a mapped drive on Windows 7. Our development team has been made aware of this issue and is currently working on a fix.
As a workaround, copy the license file to somewhere on your local system that you can browse to, such as your desktop. After installation and activation completes you can delete this file.
Alternately, you can type the full path of the license file on the network drive into the license path field (instead of using browse).