I should have included that the first step I took was to upgrade the switches to 15.7.1b4 before attempting any configuring.
This is what I did today just to see what would work:
On the 2nd switch, ran "unconfigure switch all", saved, and then rebooted to 15.6 partition. Dhcp line was gone. Changed partition to 15.7 partition, rebooted and dhcp line was back again. However, I was now able to assign an ipaddress to the default vlan. Progress.
Current config > primary switch, 15.7, no dhcp line (can assign IP). 2nd switch 15.7, still has dhcp line (but could now assign IP to default vlan). Built the stack, dhcp line is present, can not assign ip address to default vlan.
ARG!
Unconfigured stack, ran "unconfigure switch all" on 2nd switch, save config and rebooted to 15.7. Dhcp line still present in 2nd switch. For grins, I unconfigured the switch a 3rd time and rebooted. This time I left the 2nd switch a the initial config prompt. Went back to primary switch and rebuilt the stack.
Dhcp line is present, and I can not assign an ipaddress to the default vlan.
Then, I attempted what Bill had suggested in his first post. I unconfigured the stack, copied off the newly created .xsf file from second switch, edited out the line, reloaded (etc, etc, etc) and the net result was the exact same issue.
I unconfigured both switches again, and pulled the primary.cfg files off to do a side by side comparison. As expected, the difference was the one dhcp line on the second switch. I removed the line and reapplied it to the switch. Rebooted the 2nd switch and verified that the line was still gone from the config. It was, so I rebuilt the stack, and upon reboot, the dhcp line was back in the stack config and I could not assign an ip address to the default vlan.
This time, I pulled the primary.cfg off of the stack, deleted the dhcp line and reapplied the file. Rebooted the stack, and verified that the line was still gone from the config.
Set an ipaddress on the default vlan and I was good to go. Exactly what should have happened yesterday.
Thank you all for your suggestions. Why this particular switch was different than the others after the upgrade to 15.7 I can not say, However, the dhcp line was definitely there post upgrade.