Hello John,
This sounds like your problem might be related to how Safari is set up on your computer. Recent security updates for Safari now have a default setting of running Silverlight in 'Sandbox' mode. This mode 'protects' the user by restricting plugins such as Silverllight from doing certain things such as allowing it access to your file system (so you can access your files). You can adjust this setting in Safari's Preferences to take Silverlight out of Sandbox mode.
If you go to Safari 'preferences', 'Security' and click on 'Manage Website Settings' you can then select Silverlight and tell it to 'Allow' Silverlight to run in, what they are calling, unsafe mode. In the past Silverlight was allowed, by default, to run in this mode but at some point Apple changed this setting. Making this change should allow you to upload your RIS files (you will need to restart Safari after making this change).
You could check if this is the issue by trying to upload the file using EPPI-Reviewer in Firefox. If it works in Firefox the problem is most likely the 'Sandbox' issue. In that case following the instructions about should allow you to upload your file in Safari.
Could you try that and let us know if that sorts out the problem.
Best regards,
Jeff