You can do a quick check within SCD if it isn't downloading any songs. To do that navigate to "Window" > "Connection Tester" in SCDs menu.
You'll only have this option from SCD v 18.104.22.168 and later!
A new window should now popup. Click the "check connections" button to do the basic check. The test should be finished within a few seconds (depends on your internet connection speed). All the dots should change to green if they are okay or red if they failed. You can always contact me at email@example.com if you have any questions or need help with fixing any errors.
Please do copy paste the entire log which appears just below after the check has completed into the mail as well. It helps me find the problem!
Use the "Clear all saved data..." button with care! It will remove all of SCDs data from your mac! The downloaded music won't be removed!