I cannot sideload apps on my phone although I already registered for the developer free account . The account for the GDR3 OS preview . How to sideload apps for free ? It's for developement , not for illegal thingy .
I mean, what did you do to get it? Did you sign up for an app studio account? Do you have a dev account? Did you developer unlock your phone? It matters how you did it.
It won't work with the app studio, you need to developer unlock your phone. When you download the windows phone SDK, there should be something called developer unlock in it.
To side-load apps you probably need to install a certificate. After registering to App studio, you will get an email giving you instructions on side-loading your application. I hope this helps you.
Did you finish generating the app? After generating Microsoft will send you a second email giving you the link to download your app. In that mail Microsoft will send the link to install the certificate too. Try installing it. The link they sent at first did not work for me. But it worked the second time they sent me the mail confirming my app was generated.