If this is still an issue, please upload screenshots of the error, the directory that you have the netboot files in, and what software you are using for the tftp server. Also please note that if you do not hit esc soon enough, the netboot process will fail. In the netboot instructions, step 4 outlines what the console should look like when netbooting if you hit escape soon enough vs if you waited too long.
Netboot instructions can be found at http://menshen1.intruvert.com/image/netboot_1450/netboot_instructions_M1450.pdf
You will need to have a grant that can access menshen in order to download this pdf.
I hope this is helpful.
What TFTP server software are you using?
Have you extracted the netboot files from the .tgz archive on the TFTP server?
Is the .cfg file in the root directory on the server or is it in a subfolder?
You need to include the directory path to the .cfg file eg:
netboot -o -s 192.168.5.6 -f netboot/M1450/184.108.40.206/netboot-M1450.cfg
using the path from your TFTP server.
Based on your screenshot, it seems the cfg file is outside the netboot folder? What is the path to the folder containing all these folders and the cfg and netboot file?