Error 1935. An error occurred during the assembly
Wassup Greg, I believe I will be able to help you in solving your query. What you need to do to solve this problem is to uninstall the Guitar Pro 6 with the Revo uninstaller and perform a system clean with Ccleaner.
The Visual C++ is installed but fails. You need to download the Visual C++ redistributable if you do not have it as yet and reinstall it to your system.
Uninstall and reinstall your software to restart it and it should work.
You need also to ensure that you delete all the files under the registry on uninstallation.
Delete files such as the HKEY _LOCAL_MACHINESOFTWAREGuitar Pro 6 Software
Once you reinstall, ensure you also include all the files that are needed.
I hope this solves your query