When I try deploying my CloudFormation template I get "The availability zones of the specified subnets and the AutoScalingGroup do not match"

I have a CloudFormation template I'm trying to deploy. It was made for us-west-2. I'm trying to deploy it in us-east-1. I've tried making all the changes required, but I keep getting a "CREATE_FAILED" around:

Type:AWS::AutoScaling::AutoScalingGroup Logical ID: WebServerScalingGroup
Reason: The availability zones of the specified subnets and the AutoScalingGroup do not match

Below is part of my template referencing "WebServerScalingGroup".

"WebServerScalingGroup":{
      "Type":"AWS::AutoScaling::AutoScalingGroup",
      "UpdatePolicy":{
        "AutoScalingRollingUpdate":{
          "MinInstancesInService":{
            "Ref":"MinWebServers"
          },
          "MaxBatchSize":"1",
          "PauseTime":"PT5M"
        }
      },
      "Properties":{
        "AvailabilityZones":{
          "Fn::FindInMap":[
            "AWSRegions2AZ",
            {
              "Ref":"Region"
            },
            "AZ"
          ]
        },
        "VPCZoneIdentifier":{
          "Ref":"WebServerSubnetsID"
        },
        "LaunchConfigurationName":{
          "Ref":"WebServerLaunchConfig"
        },
        "MinSize":{
          "Ref":"MinWebServers"
        },
        "MaxSize":{
          "Ref":"MaxWebServers"
        },
        "DesiredCapacity":{
          "Ref":"DesiredNumberOfWebServers"
        },
        "LoadBalancerNames":[
          {
            "Ref":"ElasticLoadBalancer"
          }
        ],
        "Tags":[
          {
            "Key":"Network",
            "Value":"Private",
            "PropagateAtLaunch":"true"
          },
          {
            "Key":"Name",
            "Value": {
              "Fn::Join":[
                    "",
                    [
                      "vidly-mediadrop-app-",
                      {
                        "Ref":"EnvironmentType"
                      }
                    ]
              ]
            },
            "PropagateAtLaunch":"true"
          }
        ]
      }
    },