Because you enter the tourny when you were still an amateur ad thats where you are competing at until the tourny ends. Since then you moved up to pro and bought pro level clubs. Since you're still competing in that tourny at the amateur level, you can't use those clubs. Take them out of your bag if you want to compete in that tourny. From now on, every tourny you enter will be at the Pro level so this won't be an issue, until you make Master of course. This is done to protect players from competing against players from a higher tier with superior equipment.
Just enter the weekly CTTH until the monthlies recycle or take those clubs out to compete in those until next month ;)