This error indicates that the TFTP server has returned an "Access Denied" error (TFTP code 2).
Things to try:
* Check that you are attempting to download the correct file.
* Check that you provided a protocol while trying to download it from HTTP.
* Check the permissions on the file you are trying to download.
* Check the TFTP servers logs
* Check that you can download the file using another TFTP client, such as tftp-hpa on Linux.
* 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";
* Use tcpdump or wireshark to see exactly which file is requested