What does "svn: warning: W155010: The node is not an external" mean?

I am solving the same issue (2 years later ;-) ) Did you create and commit the folder "release_1_4_1" before update? If so, than it seems, the error you are facing arises. However, the source should be updated anyway.

It seems the solution is to delete and unversion "release_1_4_1" folder - if created - and recreate the external.