Two elements were not automatically joined.

Have you ever got the following error message in your review warnings?

“Two elements were not automatically joined because one or both is not editable.”
The expanded message may read something like the following:
Workset1 : Walls : Basic Wall : Generic 300 : id 1918731
Workset1 : Walls : Basic Wall : Generic 200 : id 2103012

This kind of error massage will only occur on work-shared projects and I tend to see it involving walls. It can happen when you edit an element and in doing so affect another element but as you have not borrowed the affected element, Revit cannot figure out, if it can join to it or not. It’s a bit of a silly warning, but if you want to be thorough with your warnings, here is how you can get rid of them.

Like always export your warnings to an html file and open it in your Internet browser.
Go to a model 3d view.
Use the “Select by IE” tool by copying and pasting the element ID numbers from the html file. Put a coma and space between the ID;s. (example : 1918731, 2103012) Press OK.
Expand “Temporary Hide/Isolate” and then select “Isolate Element”

The two elements in question should be the only items in the 3d View. The two elements may not even being touching and may be on different floor levels.

Select both elements and make them both editable. Now select one element at a time. Review its element properties to see which level it is drawn on. Go to the appropriate level. Then drag the wall end back off the walls trimming it. Now, trim or drag it back to the trimming walls. If the warning still persists; follow the same wall end dragging the trimming with the second wall.

This should eliminate the error warning.