Hi Im getting below error in trailhead "Automate Sets of Delayed Actions with Workflow"

Challenge Not yet complete... here's what's wrong: 
There was an unexpected error in your org which is preventing this assessment check from completing: System.DmlException: Insert failed. First exception on row 0; first error: FIELD_CUSTOM_VALIDATION_EXCEPTION, Please enter correct email address: []

Can somebody help in understanding what Im doing wrong here?

Hi Im getting below error in trailhead "Automate Sets of Delayed Actions with Workflow"

Challenge Not yet complete... here's what's wrong: 
There was an unexpected error in your org which is preventing this assessment check from completing: System.DmlException: Insert failed. First exception on row 0; first error: FIELD_CUSTOM_VALIDATION_EXCEPTION, Please enter correct email address: []

Can somebody help in understanding what Im doing wrong here?

I'm getting the following error in my batchable class. I want to pull all training records with an expiration date older than today and then ultimately mass update their Training Status to expired. I plan on making it schedulable. 

I'm getting the following error:

BatchUpdateTraining: Class must implement the global interface method: Iterable<Training__c> start(Database.BatchableContext) from Database.Batchable<Training__c>

Apex:

global class BatchUpdateTraining implements Database.Batchable<Training__c>{
    public String Query;

    public Database.QueryLocator start(Database.BatchableContext BC) 
    {   
        Query = 'SELECT id,Training_Status__c,Expiry_Date__c FROM Training__c WHERE Expiry_Date__c > Today';
        return Database.getQueryLocator(Query);
    }

    public void execute(Database.BatchableContext BC, List<Training__c> scope) 
    {   
        for (Training__c ac : scope) 
        {
        
        }
        update scope;
    }

    public void finish(Database.BatchableContext BC) { }    
}