Installation tends to have problems when there are old installations present, especially when a different user is doing the new installation.

In particular, it appears that the chmod() done in 'copy_file()' (as a result of the "install" command attempting to preserve the mode of files from the build tree) fails, because you can't chmod() a file owned by somebody else.

Paul Dubois suggests that simply unlinking the target file before doing the copy should work.  I think he's right, but need to think about it and test it a bit first.