No Errata
Q: When Blood Rain has been used, do Attack actions with the Dice characteristic count as having the Dice characteristic instead of the Dice characteristic, or in addition to it?
A: They replace the existing Dice characteristic – all Attack actions in the next activation use the Dice characteristic (and only that characteristic), even if they would normally use the Dice characteristic instead.
Q: When Blood Rain has been used, is it impossible to cast a spell Attack action?
A: No – remember that is always a success, so it is still possible (though difficult!) to cast a spell Attack action in that situation.