Trying to install Element 6 on iMac running High Sierra

Hi, I am new to this, but an experienced Mac user: I purchased a second hand copy of Elements 6 with the installation CD and serial number. I insert the cd and it starts installing but at the beginning, during 'system check' I get a message saying 'Installation cannot continue until nInstaller Progress is closed'. What is this? How do I close it? thanks in advance.