Is a lack of privilege, you need to Grant users access to a report server in Site Settings Options and also assign privilegesin the home folder

Grant users access to a report server

1. Go to Site Settings on the top-right Under Site settings, select Security.
2. Select Add group or user.
3. Under Site settings, select Security.
4. Select Add group or user.
5. For Group or user, enter a Windows domain user or group account in the following format: <account>
6. Click "Apply"

Grant users access to home folder

1. List item
2. List item
3. Go to the 'Security' tab and click '' and add your domain user as a System Administrator

Role definitions define a set of permissible tasks and include:

Browser Content Manager My Reports Publisher Report Builder