UR6 is the base UR for any other rollup installation. Reading into your original post I am unable to get any information UR6.May I know why you can not install Ur6 ? are you facing any issue installing that? UR6+Ur13 should be installed in your client machines without any issue , if not please wait for any other suggestions and if that does not help to resolve this error message please open a case with us and we will look into this is more details.
Thanks,
Mohammad