Can I pay the min. HBP repayment if I didn't pay into my RRSP during the 2015 tax year-Mar 2016? I get an error that the repayment amount exceeds my rrsp contribution.

If you did not contribute to RRSP's during the tax year you won't have eligible contributions to allocate to your HBP repayment. All values would be entered at zero. The tax consequence will be that your minimum repayment amount will be included in your income for the year.

So then you should be paying into your RRSP every year at least the minimum repayment in order to allocate your contributions?  Also, I have up until Mar 2017 to make RRSP contributions that will be eligible to allocate to HBP for 2016?

You are correct on both.