To clear your magic online cache, follow these steps:
1. Exit the magic online client.
2. Press the Windows key + R on your keyboard to open the Run dialog box.
3. Type %AppData% in the Run dialog box and press Enter.
4. Double-click the Roaming folder.
5. Double-click the Wizards of the Coast folder.
6. Double-click the MTGO folder.
7. Delete the Cache folder.
8. Restart the magic online client.