Ok so I found a workaround: I commented out all lines starting with <<<<< and ===== inside ui.rb and everything works fine.
you're like if commenting those lines is enough…
Is this some sort of svn malfunctioning? how did those lines get into (my copy of) ui.rb? sorry if this is obvious to svn wizards (but in that case, please drop me a word)
As Simon said before this is the way svn works (I have more experience with cvs, but the notation seems quite similar).
svn noted that your local copy of ui.rb has been modified (by you usually) and it was not able to merge your changes with those in the remote repository.
The marks (<<<<<...) you see are the way svn uses to mark witch parts of the file you have to manually merge.
If you are sure you didn't make any relevant change to the ui.rb you could delete it from your local copy and then do a svn update again… at that point svn will retrieve a pristine copy of ui.rb from the remote repository.