The issue is that the configuration for the HSRP (Hot Standby Router Protocol) group 512 on interface GigabitEthernet0/1 is not being accepted. This could be due to the use of a group number higher than the maximum allowed in the default HSRP version. By using the "standby version 2" command, it enables HSRP version 2, which supports group numbers from 0 to 4095, resolving this issue. References: Implementing and Operating Cisco Service Provider Network Core Technologies