I am in a similar boat, but with version 2.29.
I followed a YouTube video by Buffalo Americas https://www.youtube.com/watch?v=rFfLb5F9zbA to update the firmware on my 1750DHPD. When I copied my model number from the status page of the Buffalo web gui as instructed, which was actually DHP not DHPD! At the time, I didn't know there was a difference. I copied and pasted that incorrect model number into the Buffalo website search function and downloaded and installed the Buffalo software version 2.29.
Now, I've been trying all day to upgrade to a DD-WRT community version but haven't had any luck. I'm very disappointed and frustrated right now, but I'm hopeful that Buffalo or someone in the community can help me out. Any advice would be much appreciated.
I am very disappointed in Buffalo for doing this to us and you are not alone. Currently looking into buying/using routers from another vendor because of this issue with Buffalo, and they were my go to router vendor, that is now gone.
Let me try to clear up some things for you......There are two versions of this router, one is wzr-1750dhp and the other is wzr-1750dhpd and it was possible to install DDWRT on both but then Buffalo decided to lock down the wzr-1750dhp to only their stock firmware after firmware v2.27, most of us didn't know of this and they state that once you install the v2.27 you cannot go back to a firmware in which you could have installed a DDWRT version firmware on the router. Now in Buffalo's defence they have stated that they have to do this because of some agreements they signed, why the FUDGE would they sign an agreement like that and mess up the great router they sell is beyond me......had to be dollars involved....
Now the wzr-1750dhpd is the only one capable of using the DDWRT firmware. I currently own both the wzr-1750dhp(which is bricked) & dhpd routers and i have the dhpd one on DDWRT v29002 and this verison works best for me, i also used Buffalo's DDWRT v23709c then went to the DDWRT's v27805 which was okay but not close to the performance of the v29002 that i am using currently. To all owners of the dhpd router who read this, you only need the webflash.bin when flashing the wzr-1750dhpd as it is the DDWRT version.
Another thing you may not know is that if you manage to get any DDWRT firmware on the wzr-1750dhp router,this is possible but not through the normal way of flashing, it voids the warranty.
So, if you want to use the DDWRT firmware, you will need to get the DHPD version router and not the DHP once you want to keep the warranty and don't want to do something like this
http://blog.tonywall.co/2013/06/de-bricking-a-buffalo-wifi-router-with-an-arduino/