iTunes error messages.

Message says download of latest iTunes was successful but then get this message "A required iTunes component is not installed. Please repair or reinstall iTunes (-45075)" I have done this and followed all the advice in the Apple "support" but no change. Also when I connect my iPhone 4s I get this message: "This iPhone cannot be used because the required software is not installed. Run the iTunes installer to remove iTunes, then install the 64 bit version of iTunes." Have uninstalled and reinstalled - no change. Help please?