Windows Server automatically places a security restriction on cmd.exe so that the Internet Guest Account cannot access it at will. This is in the interest of security. Unfortunately, this prevents PHP from being able to run exec() commands to spawn external binaries/programs to do the tasks requested ... (such as in this case, to do backups/restores using native MySQL utilities).

To work around this, you (or the server administrator) need to alter your security configuration. Find the CMD.EXE program (usually in your windows/system32 directory) and change its properties. Under "Special Access", grant the Internet Guest Account read/execute permission.