@KajoCat
When running Fps Creator in Windows vista or higher, you have to make sure to run it in administrator mode, by right-clicking the shortcut, going to properties, compatibility tab and check run as admin and apply the settings to click okay.
Make sure to install current working entities / segments and make sure to install your model packs before installing your updates.
Hope this helps. If not, delete the whole folder (while backing up the files only, not the engine), go to your FPSC installer and hit repair, then re-install currently usable and working files to your engine such as: models, sounds, textures etc.
Your fwind ^o^ ~
Yoshondue
I am a friendly dev!~ ^o^