Real view not available in certain assembly

[aroundhere]

Realview is grayed out and only "perspective" is available under the heads up menu. Realview works fine with other models and assemblies, just not in a certain assembly. Any ideas? thanks...I have not updated it is sp0 2013.

 

[aroundhere]

looks like it was the use large assy mode toggled on. I thought I created the assy so my setting would always be the same, but I guess I didnt.