You have to build up a heavier layer of seasoning on it. One way to do that is to preheat the pan, then coat (lightly) in veggy oil and put in over on 350-375 and cook until no more smoke comes out (at least an hour), then remove pan, re-coat (I use a pampered chef veggie oil pump spray bottle to coat the pan now, but I have also used veggie oil on a paper towel) and do it again and again and again. After 3-4 times, you should have a nice black pan. Make sure the coatings are very light. You do not want a shiny black layer. That just causes problems down the road when it gets hot when you cook and then comes off on the cooking utensil. The problem with this method is it fills your house with smoke. If you have a gas grill with thermometer, and your pan will fit with the lid down, that is a great place to do the seasoning.
Another way is to cook bacon. Lots of bacon. The grease in the bacon will season the pan great. Problem with meat based grease is it can go ransid. If you go this route, make sure you wipe the pan really well when done to remove any excess.
I have some cast iron that I have treated in these ways that I can cook anyting on and it comes right out. I cook bacon and eggs almost every Sunday and the pans comes clean most times with just a wipe from a paper towel and at worst with a quick light brushing with a stiff bristled nylon brush (standard kitchen brush) in warm water and then I wipe it dry with a paper towel. When done, I then take the papertowel I drained the bacon on and wipe the inside of the pan to tranfer just a light coating of grease to the still warm pan. When all done, you can touch the pan with your finger and not come away with any grease on your finger.
MOST IMPORTANT THING: NEVER, EVER USE SOAP on your cast iron.
If it gets all messed up, and you need to start from scratch, just put the pan in the oven and "clean" the oven. That will remove every bit of seasoning from the pan and give you a clean slate to start over with.