Not sure why you are having trouble, as these boxes look to be identical. Are you saying there is no DVR button, or are you saying the Play/Pause... buttons don't work.
But this Custom Remote I built Motorola DCT-6416 III PVR should work for you. It shows a Comcast remote, but if you are with another provider I can probably change it.
I can get to the (Quick) Menu button, where DVR (along with Main Menu, Setup, On Demand, Search, etc.) is listed, but I can't get further -- when I press on the DVR button to access my recorded shows (or any of the buttons), the screen goes blank for a second (like it's going to work) and then returns me to that same screen.
Thanks for the Custom Remote link -- I am with Charter, if that matters, and I'll have to research on this support site further to figure out how to install it.
I'm new to my Slingbox 500 -- I realize that a remote for the Motorola DCX3501-M isn't available, and the closest I've found to use is the DCX3400-M, which allows me to change channels and access the guide, but not the DVR. I've also read the article, "Read this first if you have an Issue with the On-Screen Remote Control," and looked in the relevant forums, to no avail. What alternative remote do others use to access their DVR programs? Thanks!