Unable to access ISA server from new WAPS

The setup is 3 buildings, Build A&B wireless on VLAN1 can access ISA proxy for outside internet. New Build C with new WAPS are on the same VLAN as A&B. Laptop can get Ip address and access internal network but can’t ping or access ISA server. Setup static route in router to ip address of laptop works, but a route is already in for that subnet which works for Build A&B. Solution was to set a static route for that subnet on the ISA server itself. The wireless WAPS are controlled by Cisco 4400 controller. Any suggestions why that is?

Thanks