i just thought i would try 1.35na firmware and i decided i wanted to go back to 1.33na, well you cant

BE FOREWARNED.
i don't know what is the big deal about stopping you from downgrading your firmware that they lock you out of it. it never used to be a problem, pretty sure i could downgrade from 1.34na to other 1.3 firmware.
the reason for allowing people to downgrade is incase the new firmware does not work properlly. not allowing your customers to do this is just asking for trouble not to mention alienating your customers.
at work we downgrade firmware to the firmware that passed our quality tests, it also makes it easier to support them when they are all the same.
i hope 1.35 works well so i dont have to buy another router. if it doesn't you can be sure it wont be another dlink thats for sure.