I have the same problem, but under Ubuntu.
I tried to install this library but it is already installed =(
root@server:/opt# apt-get install libltdl3
Reading package lists... Done
Building dependency tree... Done
libltdl3 is already the newest version.
0 upgraded, 0 newly installed, 0 to remove and 0 not upgraded.
ZCS 5.0RC1 was running without any problems... But the upgrade does not succeed.
root@server:/opt# ls -Alh /usr/lib/libltd*
lrwxrwxrwx 1 root root 16 Nov 22 14:01 /usr/lib/libltdl.so.3 -> libltdl.so.3.1.4
-rw-r--r-- 1 root root 28K Jan 10 2006 /usr/lib/libltdl.so.3.1.4