I'm going to vote on a accidental delete with this issue. There are a couple things that can put you in the situation to "accidentally" delete it, but I have yet to find an issue where items magically vanish, or that the Revit Gremlin sneaks in and erases random information.

Sometimes simply moving a wall will cause a sketch to become invalid and would give you the option to delete. A "produce fresh" user would likely quickly hit ok and move on. Then a week down the road after the team has been working on it and someone finds it, it's tough to trace back without knowing what the actual step was that erased the item.

Obviously I don't know what your staff skill are, but that's what I tell people in my office. "I know you don't think you did, but you probably did. Let's draw it back in and see what happens."

We have had entire roofs vanish multiple times because someone moves it, and then in section it shows as a strange UFO in another users view. Well user #2 is getting ready to print and now they have a blob on their section, so the smoke it thinking that it's a rouge filled region.

They always blamed it on the Revit Gremlin. . .so I changed my user name to Revit Gremlin. No issues with that Gremlin since. . .so maybe try that?

hehe

I'm with Jasen on this one.
Somebody's deleting your floors and not admitting it.
We had a project a few years ago where the floors kept disappearing. Everybody denied deleting them.
Eventually, someone admitted "I never deleted any floors, but I did have this line is my Wall Section that I didn't want to see. But it was just a line!"
Ever since that day, when I'm teaching Revit, I tell people "That's NOT just a Line!" Very few items in Revit are "just a Line"

If you really want to dig into it (and it's happened recently), you could look through the team's Journal files. I can pretty much guarantee you'll find a line that says something like:

'************************************************* **********
'CT [Modify | Floors]: ' {1} spacer_shr
' {10} Dialog_Essentials_SketchEdit-Boundary
' {312} Dialog_HostObj_SlabShapeMainEditorBar
'
'Cache:
'
'************************************************* **********
'<<End build CT>>
' 0:< Delta VM: Avail -6 -> 8386878 MB, Used +4 -> 666 MB; RAM: Avail +187 -> 3702 MB, Used -2 -> 732 MB
'E 21-Mar-2011 13:17:01.064; 0:<
Jrn.MouseMove 0 , 669 , 473
'E 21-Mar-2011 13:17:01.064; 0:<
Jrn.Command "AccelKey" , "Delete the selection , ID_BUTTON_DELETE"

A journal file is pretty stong evedence. I'm sure anyone using it that way would be very diplomatic, eh?

Aren't the journals only saved on individuals' c: drives? (C:\Program Files\Autodesk\Revit Architecture 2011\Journals\). Or is it different with a workshared project?

I suppose a script to copy journals to a central location could be used. (Just say "it's for the children...") But what about an application that reads journals and does something (like send an alert) whenever certain commands have been used?

LOL.... ....I will follow U .

Thanks a lot....I will check out journal files onwards...Hope it will works for me.