One or more of the source document's attachment are missing

"One or more of the source document's attachment are missing" appearing for Design refresh or design copy.
Here is the way to try to fixup database without deletion of elements:
1) Create empty database
2) Set inherit design from corrupted database
3) Perform design refresh
4) On error check status bar for last design element displayed
5) Goto corrupted database and resave design element

In my sutiation main problem were with agents. So resaving them solved then problem.