
Quoting
flyingron
If you forgive the debt of more than $600 you have to send the 1099C.
Unless you're in some other type of accounting other than cash method, you don't get a write off for uncollectible rents (whether you 1099 or not).
it's just income you never received (and were potentially subject to taxes on). You just have less income to deduct the expenses (mortgage interest, taxes, insurance, maintenance) from.
If the resulting thing is a loss, then you have to determine if this is an active or passive activity. Rental by default is passive. This means you can't take the loss against other non-passive income that you have.
If you are inactive management of the property, you might be able to.
You were getting the benefit (supposedly) of the failure to be paid rent in the tax year it was due.