Page viewer webpart (set to network folder) works in ie11...but not ie9

I have configured a pvwp to point to a network folder on my app sever.

Any user running ie 11 who opens the page containing the webpart can see the contents of the shared folder.

Any user running ie 9 who opens the page containing the webpart sees a browsers error saying: Internet Explorer cannot display the webpage. If I have a user with IE 9 log in to sharepoint using a PC running IE 11 they are then able to see the content so it does not appear to be user permissions (in sharepoint or on the share) related.

Does anyone have any ideas on this?

Thank you!