1. Turn off/disable your Anti-Virus software.
2. Right click on the installer (csx767_1500.exe) and select "Run as administrator" from the list that pops up.
3. Reinstall using the "Repair" option.
4. Turn on/renable your Anti-Virus software.

When starting a new flight, I recommend you select the default C172. Once FSX/FSX:SE is ready, load the CS 767-300, and see if your problem is solved.

Note. I have added the istallation locations of FSX, and FSX:SE, to the exceptions list of my Anti-Virus software.