I think you may be having problems related to the upgrade from 8.6 to 9.0, which leads to many problems, including spurious messages about missing libraries when trying to use quicktime or the color picker. If you check your color picker, you may find it is still the OS 8.6 version, rather than the OS 9.0 version 2.1.1 Carrara had those problems you describe for me prior to the update, but now it is stable, whether saving new files/ folders to the shader browser, or doing 10 or 15 renders in a row. So you should check to see which OS 8.6 extensions and control panels you are still using, and turn off all of them except quicktime, which you might wanna update to v. 4.1