I tested it out in AdvanceMap and I know exactly what your problem is.
You don't actually need to have three warps for every doorway. It will work just fine without that. If anything, it just makes for more work because you have to direct three warps to one map, instead of having a 1:1 ratio.
You also don't have to have a black space underneath the doorway. That has no effect on it either.
I will illustrate your problem with a couple screenshots.
This is what came up when I loaded the map in AdvanceMap. This is why it goes black when you enter it. It has nothing to do with the warps and everything to do with the offset of the map itself.
To change this, you'll need to replace the map with itself. I recommend using 1.92 for this, because 1.95 always exploded in my face when I did it.
To make sure it's all good, go to the professional header mode. Just go to settings and make sure "professional header" is checked. Then look at the section that looks like this
Then, you'll need to look at the map footer offset. If it ends with a 0, 4, 8 or C, then you're good to go. If not, try replacing it again.