you have to make sure the blockland folder is in a directory that is local for the user. Windows 7 does that allow disallow stuff. It makes some programs not able to write save files and such. Try putting the whole blockland folder on the desktop or in your documents somewhere.
Also, I got the same error when I was testing for the problem
I found that going into the key.dat properties and UNCHECK both hidden and read-only
Click apply
Click ok
Try it