Dear Hakim,
The problem you are experiencing is due to incompatibility issues between AutoCAD versions, as the programmed language of AutoCAD changes time to time, when big changes are made to Operating Systems like MAC, Windows and Linux; therefore sometimes you may experience this type of probems. Please review the information on the link bellow, as is very important for the understanding of this differences between releases.
You can try to convert the .DWG files created on AutoCAD LT 2011 using TrueView, this might help you convert the whole DWG file to a newer version, making all objects, blocks and attributes compatible with AutoCAD LT 2016. I want to be sincere and also tell you that TrueView , doesn't always recover all objects on the drawing to make them compatible if they are corrupted. On this kind of cases, the objects would have to be recreated from zero on the newer version of the AutoCAD file. I really hope for the information provided to help you.
Mit freundlichen Grüßen,
Kind Regards,
Roann Knight
Technical Support Specialist
www.autodesk.com