try doing a new and reset.
Check is it only this one file or all your files?
If it is just this file, in your work environment turn on error report and see if any of the elements are causing errors.
Not enough information to do more than guess...
Erika
Architect, Consultant
MacBook Pro Retina, 15-inch Yosemite 2.8 GHz Intel Core i7 16 GB 1600 MHz DDR3
Mac OSX 10.11.1
AC5-18
Onuma System
"Implementing Successful Building Information Modeling"