Huh? Perhaps we're not talking about the same item...
I had the Kenko Teleplus MC7 as described
here and there is no focusing ring of any sort, nor is there anything macro about it.
THK Photo Products, Inc.
Perhaps you could post a picture of the teleconverter that you have. As you mention it having a focusing ring, I'm guessing perhaps might have an older version that is similar to the Vivitar macro teleconverter, that has a helical focusing ring. If the focusing ring is stuck, it could be something is seized or the helical threads might be damaged, or there is something that is preventing it from turning.
If it is similar to the Vivitar 2x Macro teleconverter, I believe it is best mated to a 50mm lens, and not a zoom like the DA 16-45mm. At any rate the DA 16-45mm already focuses very close on it's own. I'd suggest you determine if the focusing ring can turn without any lens mounted first. One thing is for sure, nowhere does Pentax recommend nor guarantee that the said teleconverter/DA 16-45mm combo will work.