I have recently experienced the exact same issue. We have over 40 AP's in our building, some are R700's the rest are 7982 zoneflex. I had the exact same issue with some brand new HP laptops. They would connect to the 7982's fine, but as soon as they were connected to an R700 AP the lapotps would take an age to log in and often fail altogether. The Zone director would show authentication errors for these devices even though the Key was correct.
In the end i disabled the 5ghz range on the R700's and i have not had an issue since.
