Make sure the folders not read only.
Are you running Windows Vista?If so, you need to move your Blockland location out of C:\Program Files or Program Files (x86) and put it in C:\ and change the shortcut on the desktop.Vista has this odd working where it won't let some programs rewrite stuff in Program Files to avoid malicious stuff happening.
I have XP.
Bump, I really need help.
Chances are, the best way to avoid this is to just save the bricks into a different file, then open up Blockland\Saves and get rid of the old copies as needed.