New router- IE can’t autodetect proxy

Hired a guy to replace a Cisco 1601 (IOS 11.2) with a Cisco 2600 (IOS 12.1). He cut and pasted the 1601’s config and made a few modifications, but not much.

Now, desktops cannot access the internet unless I manually configure IE proxy server settings. All other IP apps are fine. He has suggested that I update the ARP table on each PC by pinging the router manually. I tried that yesterday on a PC and it did not resolve the problem, plus, unfortunately, most of the computers at that location are Macs, so pinging at the command line is not possible. Now he is suggesting that there is a DHCP problem, but I made no changes to DHCP. Also, I can see that DNS is resolving IP addresses, so that is working. Any suggestions?