[CentOS] virDomainSetMaxMemory error

CentOS 5.6, x86_64

In Virt-Manager, when attempting to either change a guest's memory allocation or even just clicking "Apply" on the memory tab and not actually changing the values, the following error pops up:

"Error changing memory values: this function is not supported by the connection driver: virDomainSetMaxMemory"

When Googling around, I am finding reports of this error as early as two days ago, and as late as a year ago. Is there an option in KVM/Virt-Manager I am missing in order to resolve this problem, or is this bug really over a year old and not fixed in CentOS 5.6?