I had a complicated assembly.  Everything looks fine.  No warning no error on the assembly and drawing.  When I modified the drawing yesterday, I hide a decal sketch on the drawing.  That was all I did and saved the drawing.  When I open the assembly and drawing today, there are red error messages on my assembly and drawing.  I don't know what happen so I reboot my PC and that did not fix it.  Solidworks 2012 scares me. .  Any advice how to fix this please?  Thank you