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 the permissions on the file you are trying to download.
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