1. Make sure you have the appropriate VR (Virtual router) mentioned to the command executed.
If you have connected a PC directly to the management port and trying to perform the action then please mentioned vr-mgmt if not vr-default.
2. Make sure you can ping the TFTP IP address from the switch.
Note: The ping command defaults to VR-Default so if your using the management port make sure to select VR-mgmt in the ping command.
2. If you're running a TFTP server on a PC try disabling the firewall in the PC.
3.Try using a third party TFTP program like TFTPD32, or TFTPD64.