linked list allocation...problem with heap

I am creating a linked list that contains a int* and a next*. I create two different lists, the first one contains about 500 nodes, however, when I try to create the second one, I only get about half way through, about 150 nodes, when I get a "NoMansLand" error; this happens when windows checks the integrity of the heap. Both lists look good when I run it through the debugger, my lists is intact, but I can't figure out why i'm getting the "NoMansLand" error. It happens in debug mode, I haven't tried running it in release mode yet because it will take a good bit of config changes. Any ideas?