user1809: I can't enable Motion Blur on this layer:

Any ideas what could be wrong?

user1909: If you right click your "loader"-layer and choose Pre-Compose Layer and choose Move all atributes into the new composition, you should be able to put motion blur on it.
And just a tip: If you for some reason in some situations can't use blurs, often because of motion generated by effects, you can use CC Force Motion Blur to force motion blur to your footage.

user2197: 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. 

1809: <p>I can't enable Motion Blur on this layer:</p>

<p><img src="https://i.stack.imgur.com/6moQz.png" alt="enter image description here"></p>

<p>Any ideas what could be wrong?</p>
 1909: <p>If you right click your "loader"-layer and choose Pre-Compose Layer and choose Move all atributes into the new composition, you should be able to put motion blur on it.</p>

<p>And just a tip: If you for some reason in some situations can't use blurs, often because of motion generated by effects, you can use CC Force Motion Blur to force motion blur to your footage.</p>
 2197: <p><strong>Thats because you have the collapse transformations button ticked:</strong> 
<img src="https://i.stack.imgur.com/1lkHW.png" alt="Collapse Transformation"></p>

<p>When <a href="http://help.adobe.com/en_US/AfterEffects/9.0/WS064964FC-424C-4e5a-A5C3-2160B3DFBCA4a.html" rel="noreferrer">collapse transformations</a> is ticked After Effects takes the options of the layers <strong>inside</strong> 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.</p>

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