If I'm reading it correctly it looks like you are putting a block element <ul> inside an inline element such as <span>, which isn't valid code... Move the block element and place it outside of the inline element...
That's correct. It means you're trying to wrap an inline element over a block one. Move your block element (un-ordered list) before the inline element's opening tag and be sure to close it before you close your list.
I have not put any block element inside an inline element..check the code... <p> <ul> <li><b>Adsense for content<b>...
Which site is it you are trying to validate? (It's not the one in your sig is it?) It would be much easier to see what the problem is by looking at the code...but it does sound as if you have a block inside an inline. Nick