Staining wood

I am attempting to stain one of the pocket doors in my house.  It was an unfinished door that I have been trying to ignore.  I got out my power sander, sanded it thoroughly, wiped down the dust and started to stain.  There are several places where the stain is "taking" in a blotchy manor.  Some places are too light and some are too dark.  This is not the first time I have stained something so I do have some experience.  I just can't figure out what is going wrong.  I am going to let it dry for 24 hours and then hit it again just in the spots that are noticeably too light.  My fear is that the door may be poplar and it will never take the stain correctly.  If I try another coat and it still doesn't work, I am going to just paint the darn thing.  That will mean it will need sanding again and a coat of stain blocking primer BEFORE I can paint.  I am going to be really cranky if this door ends up having to be painted!