This error usually indicates that you have tried to open a URI using a protocol that is not supported by your current build of iPXE.  For example, if you try to boot from an ''%%ftp://%%'' URI in an iPXE build without ''DOWNLOAD_PROTO_FTP'' enabled, then you will see this error.

You can see the list of supported protocols in the iPXE startup banner.  For example, if the banner shows

    iPXE -- Open Source Network Boot Firmware -- http://ipxe.org
    Features: HTTP iSCSI DNS TFTP AoE bzImage COMBOOT ELF MBOOT PXE PXEXT

then you can see that FTP is not supported by this build.  (Supported protocols for this build include HTTP, iSCSI, and TFTP, but not FTP.)

Things to try:

  * Check that the URI that you are trying to boot from (in particular the protocol name before the first colon) is correct.

  * [[:download|Rebuild]] iPXE with the protocol you want to use enabled.  (You can edit the list of enabled protocols in the file ''config/general.h'' within your iPXE source tree.)

  * If you are trying to boot via TFTP, and you are not specifying a full ''%%tftp://%%'' URL as the boot filename, then check that your DHCP server is handing out a ''next-server'' address.  (Newer releases of [[:howto:dhcpd]] do not set this address by default.)

  * Oracle(r) VirtualBox (YMMV, 4.2.6) ships with a stripped down version of iPXE with several features disabled. The [[howto/dhcpd#PXE chainloading|typical method for chain loading]] from a vendor ROM is to use a conditional to identify the DHCP user-class option as "iPXE". This method does not work when the vendor ROM is iPXE and missing features you might need. This issue can be worked around in one of two ways. iPXE sets [[howto/dhcpd#iPXE-specific options|iPXE-specific DHCP options]] for features that have been enabled. A conditional can be set up ([[https://gist.github.com/4008017|example]]) to check for these options and if missing, to chain boot to a full featured iPXE. Alternatively, [[https://git.ipxe.org/ipxe.git/blob/HEAD:/src/config/vbox/README|the VirtualBox iPXE ROM can be replaced entirely]]. On supported platforms Oracle(r) VM VirtualBox Extension Pack, which provides Intel PXE, can be used to replace iPXE.

  * If embedding a certificate to verify a HTTPS server with this can be caused by incorrect certificates being embedded in the iPXE binary. When this is the case rebuilding the iPXE binary with the correct certs should fix the issue.