This is the only bit you need to take note of (I re-worded it a bit too
1) Select any parts of the map that you have copied & pasted and delete them (This will stop the problem from occuring again in this map)
2) Then save. Then select all actors and delete them.
3) Go on view -> Actor properties, if the titlebar says 'Brush 1 selected' then you are in the clear (that's the builder brush that's selected).
4) If however, it says that there are more than 1 actors selected, go on display and set the drawscale to 20 so that you can find where they are.
5) Any that you find are corrupt and you need to remove, take note of the position of as many as you can. (Don't delete them yet)
6) Now press undo untill all your actors are back again.
7) Select the corrupt ones (now that you know which ones they are) and delete them. They won't appear to go away but don't worry.
8) Save you map (as a different version to be sure), close ued, then load the map up again and they should be gone.
To double check that you got all the corrupt actors, repeat steps 2 and onwards.
If you did step 1 right and deleted ALL parts that you have Copied & Pasted in your map, you should not have anymore corrupt actors appearing from now on
