Hi,

Recently I've been modeling some of our equipment that is basically made up of various structural members, ie. a couple pieces of tube steel bolted to some c-channels.  For some reason when I make my assembly everything looks fine, my parts have the right holes and are the right color, but then I'll close the assembly and open it a moment later and several of the members are greyed out and are missing all of their holes and I have tons of errors because all of the bolts have lost their concentric mates.  I can't seem to figure out why this is happening all of the sudden.