An annoying PROBLEM

whenever i write up something and go to preview it but forget to enter my password i am told to go back and enter it, unfortunately when i go back my message is gone.

You might want to enable cookies :)

they are. this only happens when i preview not, when i forget my password and then post.

I don't know why that is happening to you, but one solution might be to skip the preview. You can still edit your post after it has been posted if you see an error.