I'm not a rose grower, but since no one else has come forward, from my reading, it seems like the likeliest culprit is rose midges.
Here's a nice little article on diagnosing rose problems:http://www.olyrose.org/pests.htm
If you scroll down a ways you will find this
(Problem) Roses fail to blossom or existing buds suddenly turn black and die. The foliage and the stem surrounding affected buds may also blacken and die. (Cause) Rose midge, a fly larva that is white and 1/12 inch long. The larvae feed in clusters at the bases of rosebuds.
Note 1/12" is very tiny. These will be hard to spot, look carefully at the bud base.