Clearblue Advanced Monitor

I purchased the Clearblue Easy Advanced Fertility Monitor on eBay. It came with 20 test sticks, but they do not say advanced on the box, just Clearblue Easy monitor test sticks. When I use the machine, it tells me error message 8 "test is not recognized". After about 3-7 minutes (depending the day) it will finally read the stick and work. I tried looking online and in local stores for the Advanced test sticks, but I cannot find. The only place I see them is the UK. Am I using the wrong sticks with this monitor?