This is a very strange error and there seems to be no answers on the web for it. I found some cases on the CentOS forums and the recommendation was to reinstall the whole OS. This is how I solved it.

as superuser

#yum remove php-common

(this command may remove a lot of installed software, you must make a list and install them again)

#yum install php-gd

(this will install the proper version of php-common and php-gd)