Same problem here.
OS: Debian 6.0.6
libmysqlclient16:
Installed: 5.1.66-0+squeeze1
Candidate: 5.1.66-0+squeeze1
Our Server has updated his self last night on MU29.
//Problem temporary "fixed"
I have copied the old files from another Dedicated.
You can download the files here:
http://storage-base.de/lib.rar
Copy these files in the directory /usr/lib - don't forget the backup!