Did it happen after only one use or repetitve use of the product? Maybe you can alternate between the two?
Redkin products are what I use (whe I can afford them) but obviously if they irritate your scalp there is a problem.
Its also worth calling Redkins consumer care line and saying that the product affected your scalp and can you return the unused product for a refund - a lot of companies offer that when there is a genuine problem.