"Сок клюкв" as well as "Cок виноградов" makes little sense. It sounds like "oranges juice"/"the InternetS"/"I brushed my hairS"/etc. Counting does not work this way.
Name:
Anonymous2010-07-14 2:29
also "сок клюква" makes no sense at all. In this form it's just two nouns that are not related to each other in any way.
Name:
Anonymous2010-07-14 18:36
Клюквенно-виноградный сок
Kliukvenno-vinogradnyj sok