When you start developing Windows Store Apps you are automatically guide through the process of acquiring a developer license, but they will only last for 30 days.

For example:

If you try to run a Windows Store App on your PC that you deploy from Visual Studio after the 30 days you get this error "Your developer license has expired. To continue to use this app, please renew your license."

To fix this follow these steps.

Open up an existing Windows Store App project or create a new one.

Go to Project --> Store --> Acquire Developer License.

Sign in using your Microsoft account

Click I Agree

 Finally you should receive this dialog

Click Close