When running the svn update command, you may get this message:
svn: E155007: None of the targets are working copies
This is because you need to check out the solution to the folder. If it used to work but doesn’t now, you probably deleted the hidden .svn folder which contains all the information about the solution checked out to that folder. In the latter case, if you restore the .svn folder then re-run snv update, it should work.