I encountered the same problem.  I loaded a song that contained SI Bass and the SI Strings and got a message saying that the SI instruments were missing or not installed properly.  All the folders for the SI were present in my computer but Cakewalk by Bandlab did not scan the VSTs properly.  I really don't know if uninstalling and reinstalling Cakewalk by Bandlab would have solved the problem but I definitely couldn't reinstall the SI Suite because the addon install of the Studio Instruments Stu