Scrape off the excess with a wax comb then use mineral turpintine , then use soapy water to remove the turps, after that use some metho, I have done this twice and a big tip is to do it properly the first time and be extra thourough because you don't want to be out having a lovely paddle around and your deck grip starts to float away [}:)] trust me I know !!.
Now if it doesn't adhere then you need to go to Bunnings a get some "fast grip" contact cement (not the "gel" one) just the regular contact and make sure your grip and board is completely dry apply to bothsides with a brush let it go tacky (around fifteen minutes) stick it down and its on for good

do it in sections maybe a third at a time thats if the whole lot comes off if not make sure you pry it up gently to where has stuck and dry it off or the contact will go mushy as I say nightmare!!

To avoid this nightmare clean it off really well the first time and you won't have any probs.