Hi. We tried to figure out what could be the problem but unfortunately we can’t. That’s Proteus problem, it’s not microcontroller code problem. Even though you used the router IP address for your ENC28J60 which is wrong, you should use your computer IP address as the host in ENC28J60. But the IP address cannot cannot halt the simulation.
I suggest you ask that question in another forum especially a forum dedicate to Proteus, People with more knowledge with Proteus might assist.
And if you find the answer, please share it with us here in the forum, it might assist others as well in the future.