Yes, I've been completely stopped in stage 6. Obviously there is something I'm missing here, but I've tried everything and am still stuck three days later, which has ruined my fun with this game.
The stage in question has three ghosts. The middle and bottom ones I can get, no problem. The one at the top, however, floats right under a painting and a table. There is another table below the ghost that seemingly makes it impossible to get a proper angle of attack.
I've read the in-game directions multiple times to see if I was missing some control or feature. I like this game but this stall has ruined my fun.
I'm almost just as afraid to find out the facts, as I'm sure I'll be kicking myself over the simplest thing I've been overlooking.
For stage 6, throw a bomb up so that it bounces off the lower picture frame. It should bounce off the higher frame and into the ghost's mouth. It may take a couple tries to get the angle right. I am on stage 39 now and in general you will do well if you are not afraid to bounce bombs off obstacles and the walls. Hope this helps!