In navisworks manage 2013 everytime I build a model and refresh the appended drawings everything disappears. The selection tree shows question marks for all the drawings. I have rebuilt the model a few times and done an audit on all the drawings.
Please make sure you have applied the latest service pack to Navisworks 2013. There is a known bug in the original release of Navisworks 2013 when using the Refresh command. The bug was fixed for Service Pack 1.