This was getting outside our expertise, so we ended up engaging our developer and his investigation led him to the following conclusion:
The system our server is running (CentOS 5.5) is no longer in active support and so cannot get updates through Yum (the package manager & software repository)...
Plesk failed to update automatically. I tried searching the forum 1st for text from the update logs, but was unable to find anything related to my problem. Can someone please help or point me in the right direction?
Message in Plesk Panel: "Failed to update Plesk. To solve this problem, you can...