I ran into the same problem with Ubuntu 14.04 where MLDonkey Core is compiled with glibc 2.18 but running with glibc 2.19. You can compile and install the package again to solve this problem.
sudo apt install debian-keyring dpkg-dev
sudo apt-get build-dep mldonkey-server
apt-get source --compile mldonkey-server
sudo dpkg -i mldonkey-<Tab>.deb
The first line is needed to check package signatures and uncompress source packages. The second line installs compilers and headers to compile mldonkey. The third line downloads the source and creates the package. The fourth line installs the new package (press Tab to autocomplete the filename as the filename will depends on mldonkey version). You can then delete all mldonkey* files and folders in the current folder.