I'm sorry to hear that your Slingbox Solo stops at 25% during the update.I do understand that you have already tried a few troubleshooting steps on your end and you are using a MAC. I will be attaching a helpful link to solve your issue. In order to proceed with the software update and reconfiguration of your Slingbox Solo, you will need to use a Windows computer. Please review the link below for further reference:
Sling Media Support!