Wifi works in Bootcamp but not in Mac OSX?

Due to the location of my computer in my new house, I need to use Wifi on my iMac (Late 2013, El Capitan). The Wifi works great when I boot the iMac into Windows10 using Bootcamp, but in El Capitan I get this error:

"The Wi-Fi network could not be joined. Try moving closer to the wireless router. Alternatively, run Wireless Diagnostics to troubleshoot."

I moved my computer right next to the router and I still get the same error. I ran diagnostics and got no help. Again, Wi-Fi works great on the same iMac when I boot into Windows 10. The internet works great in Windows 10 and El Capitan when plugged in, but due to the location I can't use a network cable.

Any ideas?