I've found this error in my logs:
relocation error: /usr/lib64/libmyodbc5.so: symbol strmov, version libmysqlclient_16 not defined in file libmysqlclient_r.so.16 with link time reference
yum-error-log
yum install mysqlclient16
...
184 packages excluded due to repository priority protections
Setting up Install Process
Package mysqlclient16 is obsoleted by mysql-libs, trying to install mysql-libs-5.1.59-1.el6.art.x86_64 instead
Package matching mysql-libs-5.1.59-1.el6.art.x86_64 already installed.
Checking for update.
Nothing to do
i've used the atomicrepo using the latest mysql-version (mysql-5.1.59-1.el6.art.x86_64) on a server driven by CentOS6.
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Plesk: This also appears in Plesk 10.3 > Application Vault as "Error 500"
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edit: i've posted my solution as a response, maybe somebody will need it