Thank you for including the full output of your procedure, and not just the error message (or even worse, a paraphrased version of the error message!) Having the full details is greatly improves the chances of figuring out what is happening.
potentiometer:
linino> setenv 192.168.128.44
linino> setenv 192.168.128.45
I don't believe these statements are accomplishing anything. I think what you intended to enter is:
linino> setenv serverip 192.168.128.44
linino> setenv ipaddr 192.168.128.45
The setenv command sets an environment variable (given by the first argument) to a value (given by the second argument.) For example, the last statement above sets the variable "ipaddr" to the value "192.168.128.45". In your statements, you are only including one argument, so you are defining the variable "192.168.128.44" and giving it nothing as a value.
What you are trying to do with these statements is define the IP address of the Yun, and the TFTP server it is to contact to download the software image. Without the serverip and ipaddr variables being set properly, uboot uses default values to contact the server:
TFTP from server 192.168.1.1; our IP address is 192.168.1.2
I would retry the process, but make sure to enter the setenv commands accurately.