I've never seen that error message, so I have to guess what might be wrong. I would guess the software you're using to produce the SCC file messed up somehow. I use Annotation Edit from Zeitanker.com, and if this happened to me, I would try a new export. Then I would try exporting the captions track that Annotation Edit produces when the Caption Test is run successfully; it always makes a new copy of the Captions track if there are no overflow errors, and the timecodes on that will be a few frames different, to optimize playback. Often, that Caption Test track works better than the human-produced one.
Finally, I would try re-importing the problem SCC file into Annotation Edit, and then export a fresh SCC from that.
Whenever I receive caption errors from DVDSP, it is on Build, not import of the SCC file, so I'm at a loss what could be the issue you're experiencing.