The registry error usually is an indication that the software was not installed as an administrator  

1) Go to the file mecawindinstall.exe  

It can be downloaded at

2) On your Mouse, Click your RIGHT mouse button 

3)  A drop down menu appears and you select 'Run as Administrator" 

4) Go through installation, you simply need to install this OVER your existing installation, no need to Uninstall the previous installation.

When you run the software in subsequent attempts, you won’t need to be an administrator, this should only be required during the installation.   If you are not seeing the Run as Adiminstrator option, then you need to verify that you are in fact logged in as an administrator on your computer.  Below is a video illustrating these steps:

Video Illustrating how to Run As Administrator: