I was getting this error while adding my project in SmartSVN and I had no clue whatsoever
*directory* is already under version control SmartSVN
The reason I was getting this error was because I had select the root folder and the sub folder and choose to add the files recursively . That basically added the sub-folder two time, one time as part of recursion and a second time because it was explicated added.
Simple solution is, select only the root folders and click add *recursively* or select all folder and choose to “Only Add Directory”. The first solution worked better for me btw. Hope this helps someone.