Installing new AVG Internet Security

I tried many times to install a newly purchased AVG Internet Security' but evrytime I get a message that this is not compatible with prevously installed AVG protection?? What does this mean? I have an AVG Zen (Free Version) installed currently.

Hello Ashwani,
We understand how something like this can really try your patience.
Please be informed that it is advised to install one Antivirus in single pc. If two or more antivirus is installed in single pc, it will conflict your pc. That is the reason AVG Internet Security is not been installed in your pc. We request you to uninstall AVG Zen http://avgclick.me/UninstallZen and then install AVG Internet Security in your pc to get this issue fixed. To install AVG Internet Security please click on the following link http://files-download.avg.com/inst/mp/AVG_Internet_Security_742.exe download and install the file. Also the license number has been sent to your registered email id. Please feel free to contact us for any further assistance. Thank you.