Just restrung my guitar with D'addarios Drop C strings, but i'm having a few issues

I can't get the strings to reach their correct pitch, (e.g. the 5th string refuses to tighten past Eb, when it's supposed to be a G, 6th won't go past Bb)

Anyone know what i'm doing wrong? I restrung my S570b with 10's, and had no problems at all (really good move as well, i'd recommend it to anyone)