I've commented on this problem before somewhere in this thread. The problem is probably that you use a 64bit distribution which doesn't have a 32bit version of libmpfr available. The solution is to link to another file that seems to be binary compatible. The exact steps are mentioned in that older post of mine
Mmh, I am pretty sure I have a 32bit Ubuntu.
I've got libmpfr.tar.gz here(PokeParadox linked it somewhere) so maybe you could just tell me where to place it?