Recognize "TX not possible" exception

monero/backends/jsonrpc.py

@@ -174,6 +174,7 @@ _err2exc = {
     -2: exceptions.WrongAddress,
     -4: exceptions.NotEnoughUnlockedMoney,
     -5: exceptions.WrongPaymentId,
+    -16: exceptions.TransactionNotPossible,
     -20: exceptions.AmountIsZero,
     -32601: MethodNotFound,
 }

monero/exceptions.py

@@ -21,3 +21,6 @@ class NotEnoughUnlockedMoney(NotEnoughMoney):
 
 class AmountIsZero(AccountException):
     pass
+
+class TransactionNotPossible(AccountException):
+    pass