Not able to use case comment object.Initially we write few lines of code on case comment object and it was working. But, now when we are trying to change the code its is showing invalid variable commentbody error message. Then i  reverted all the changes and just tried to save the method as earlier. But now also im not able to save that class. Same code is not giving errors in UAT but getting error in Dev sandbox. 

   public static void UpdateCaseComment(string Id, string comment ){
        casecomment cc=new casecomment();
        cc.Id=Id;
        cc.commentbody=comment;
        try{
            update cc;
        }catch(Exception e){
            System.debug('er->'+e);
        }
    } 

This is my code 
Please let me know what is causing this issue.