is it very old? We found that milk older than a certain number of months was like that, and ended up tossing a lot.
It hasn't been kept in the freezer much longer than we've kept milk frozen in the past. Could be it's from a time when there were supply issues (happens here occasionally) and it may have been previously frozen or run into other issues before it got to us. Regardless, I'd like to avoid throwing it out, if possible.