Recently, the VoxCeleb corpus was updated, and the speaker IDs were changed. My guess is that you're using this newer version of the corpus. Updating the recipe to handle both older and newer versions of the corpus is on our list of things to do.
Fortunately, fixing this on your own is quite straightforward. You have to write a script that converts the speaker IDs in the trials to the new format, or, equivalently, write a script that converts the speaker IDs in the data directory into the old format.
This file will probably be helpful for you:
http://www.openslr.org/resources/49/vox1_meta.csv. The first column is the newer speaker ID format, and is probably what you're using. The second column is the old speaker ID format that the trials file expects.