Comment Not a grammatical error (Score 3, Informative) 312
The plural attributive construction is well established as standard, and has been on the rise for the past 70 to 80 odd years. It's standard everywhere, but is somewhat more common in British English than American English. If the OP were interested, they could read about this topic in A Comprehensive Grammar of the English Language (Quirk et al 1985), where it is covered starting on page 1333, although somehow I doubt they're interested.