I'm noooooo expert here! But I recently have had some experience and I could possibly offer advice. Sounds to me that this could be canker infecting your cuttings. Canker is a nasty Springtime ailment. It occurs when fungal spores get into the open wounds on roses and infect them, turning them black. Sorry to say, but depending on the damage to your cuttings, they could well be ruined. Even if they start to produce, they may not produce the best bushes in the long run. I'd wager any bushes from them would be weak. But that's my guess.
In future, when you make cuttings you can help minimize spored damage by making sure you cut a diagonal, and always cut near a leaf node so that the cutting has a chance to calcify there.
You might be able to save the cuttings if you have enough healthy stem left on them though. Someone else could probably tell you better.
Currently, I am experimenting on the use of Elmers glue on the pruning sites, I know this helps to prevent cane borers, and I'm curious to see if it will also prevent canker infections.

Good luck!

Could be that the environment is too moist (i.e., wet). You might try my method, outlined in post above (about MGleason and GMander). I almost never get black/rotted cuttings anymore. Hope this helps. GaryStPaul