The message might either means the Simconnect installer has reported an error, but also a corruption of some of your XML file. Unfortunately, you don't say which exact version of P3D V3 you are installing, and this is important, since the installation method is very different between the latest 3.4 and every other version before.
It's possible to log the installation, to know more precisely at which step the error occurs, this way:
- Open a command prompt ( Start->CMD->Enter ) and go to the folder were the installer file is located (cyvr_fsx_setup.exe) , and type the following:
cyvr_fsx_setup.exe /LOG=logfile.txt
Run the installer and wait for the error to appear. A log.txt file should have been created in the same folder. ZIP it and send it to me by EMAIL, using the small mail icon under the fsdt logo in my forum avatar.