I'm having the same issue as well with P3D V4 installer. It downloads the install file just fine by the looks of it. However, when I go to install GSX, it gets stuck installing the textures saying the file source is corrupted. I've searched the forum and found other users with issues and followed their steps, but to no avail I cannot get this error to go away. I've tried everything I can think of to resolve it.
Thank you to anyone who can help!!