Windows Firewall Blocking Traffic:

The firewall on the Windows VM might be configured to block incoming ICMP traffic (ping requests). By default, Windows Firewall is set to block ICMP traffic, which could be a reason for the connectivity issue (Option A).

Security Group Configuration:

AWS Security Groups act as virtual firewalls for instances. If there is no rule allowing ICMP traffic in the security group attached to the Windows server, the ping requests from FortiGate will be blocked. An inbound allow ICMP rule must be added to the security group to permit this traffic (Option D).

Other Options Analysis:

Option B is incorrect because the default AWS Network Access Control List (NACL) allows all inbound and outbound traffic.

Option C is incorrect as AWS does allow ICMP traffic between subnets if properly configured with Security Groups and NACLs.

References:

AWS Security Groups: AWS Security Groups

Windows Firewall Configuration: Windows Firewall