Props showing up as error?

After a couple of days working on my map I loaded up to continue work although I noticed that some of the props had become "ERROR" signs and were not showing up or active in their collision model when I ran the map. I'm quite stumped since this is the first time I encounter a problem like this. (The most notable prop that was affected were my barrel crate props)



EDIT: The problem went away after I uninstalled and reinstalled TF2 sorry if I took time from anyone.