In Google Analytics, there are three entities: Account, Property, and View. In order to link and view your Google Analytics metrics in AdStage, you must have "Read and Analyze" access to the entity you wish to view.
If you aren't sure what permissions you've been granted, ask your Admin to follow the below steps. From there they can confirm you have Read and Analyze, or grant you permission.
Step 1: Log into your Google Analytics account.
Step 2: Click on the Admin tab.
Step 3: Click on User Management.
Note: In Google Analytics, there are three entities: Account, Property, and View. AdStage supports access to any entity as long as you have "Read & Analyze" permissions to the entities you wish to view.
Step 4: Make sure the user in question has "Read & Analyze" permissions checked.
More info on Google Analytics permissions can be found here.