Yes, I installed it, as root.
(I gave "su -" for becoming root and issued "make install" from there.
I noticed that installation is optional and upon a successful compilation I could fire "solarus_run" from the build directory, so I did it (before installation).
It gave me the same output (solarus_run: error while loading shared libraries: libsolarus.so: cannot open shared object file: No such file or directory).
Just a question here: Is libsolarus library x64 arch?
If it depends on 32bit binaries, it could explain this message (because latest ia32 version on xUbuntu systems are more or less, broken).

(32bit is a foreign architecture at my system).