Justin, the ROP is a very demanding program. For that reason, when asked, I generally advise people to err on the light side when choosing a weight.
It would be helpful to have more information, e.g., what else are you doing? The program works great if your other days have nothing strenuous in them at all. Pavel explains what he means by "variety" but I find many people do too much or go too heavy (or both) and then the program itself suffers.
It would also help to know where you are in the program, e.g., if you're close to the end, I might advise adding in a few extra rest days to allow yourself to finish, but if you're not, then it might be time to reevaluate. When a proven program like the ROP doesn't work for you, it's good to ask why. I've done the ROP several times myself, and I think the ROP might be the closest to a "sure thing" there is. Let's see if we can figure out _why_ you're having a problem! and then figure _what_ to do about it.
-S-