There are only two possibilities why the amount would be taxable: (1) it's a rollover to a Roth IRA, and (2) you rolled it into an HSA using the once-in-a-lifetime contribution feature, and then all of it wound up being an excess contribution. Each of these possibilities has its own question of you in TurboTax after you've entered the 1099-R. First, you'll be asked "Was this money rolled over to a Roth IRA" and you'll have to check "no." Then you'll get the HSA question which must also be checked "no" (if applicable). Double check these and let me know.
