Change <zero_debts>1</zero_debts> to <zero_debts>0</zero_debts> or just remove that whole line.
From the BOINC Wiki: Client configuration:
<zero_debts>0|1</zero_debts>
Set resource scheduling debts to zero. This lets you fix situations where client bugs have resulted in distorted debt values. Set it, run the client, then clear it (otherwise you'll start out with zero debts every time you run the client).