illegal TFTP operation from WDS-Server

i would like to use TFTP-Server part of WDS-Server for delivering default config-files to our switches.

i setup DHCP option 66 to ip of wds-server and i see tftp-requests for default-config-file on wireshark. but wds-server answers always with error code 4 and message access-violation. the default-config-file exists on tftp-root-path and is readable by everyone. it's a simple text-file.

there is no image for pxe-boot or windows-deployment required.

thanks for any help.

Heiko