Try resetting AutoCAD 2013 to defaults by clicking Start > All Programs > Autodesk > AutoCAD 2013 > Reset Settings To Default. It will let you save your current settings first.
If that doesn't help, make sure you can reproduce the error in a brand new drawing. We want to make sure the issue is not coming from a specific drawing. I would then run a repair of AutoCAD and if that doesn't fix it, uninstall and reinstall the program.
Let me know how it works out.
I'm glad you were able to fix the error! Was it resetting AutoCAD to defaults that did it or was it repairing the program?