This error indicates that the TFTP server has returned an “Access Denied” error (TFTP code 2).
Things to try:
If you are using qemu's embedded TFTP server, try adding an extra leading slash to your filename (to work around a known qemu bug). For example, if your
DHCP server is currently handing out
filename "pxelinux.0";
then try changing this to
filename "/pxelinux.0";