Julian Bennett's late goal salvaged a point for the Reds after another difficult afternoon for boss Gary Megson at one of his former clubs.
Grayson said afterwards: "I'm very disappointed not to have won the game. At 2-1 up you should really kill the game off.
"I think a little bit of a lack of experience has cost us - we kept looking to win the game 3-1 or 4-1, but perhaps we should have just kept the ball in the corner.
"We got two great goals and Marcus Bean did ever so well as he only passed a fitness test at lunchtime.
"We made two mistakes to allow them back into it and I am disappointed - I feel like we lost the game."