Can't add Motion Blur to layer imported from Photoshop
Thats because you have the collapse transformations button ticked: 


When collapse transformations is ticked After Effects takes the options of the layers inside the 'loader' composition. So you will need to open up the 'loader' composition (double click) and then you can enable motion blur on the layers inside.

When you import Photoshop documents into After Effects as compositions, any groups in the PSD become pre-comps within AE.