Cannot load the document contents in PTC Navigate View Requirements App

Hi, all.

I imported PTC Navigate ALM extension and tailored View Requirements App as below.

When I try to search Requirement Specification Document which has only text, it works fine. However, if it has an attachment file like PNG or VSD, it cannot load the document. Other types of document work the same. Did I misconfigure something or need to configure something else?

Thanks,

Yeayoung