View source for Backup & restore

I'm trying to backup and restore my site via the admin panel. The backup seems to be working fine but when I click on Restore, I didn't see any backup and I have the following message:

You can restore any of the backup packages found or remove it from the server.
%%(info type="error")Problem The file/backup/ directory is not executable.%%

Can you tell me why this is happening. My wicki is installed in a Windows environment.

Thanks in advance.