i have written a class for Case merge functionality , But the problem is when ever i call this class from trigger it shows error .... can anybody help me how can i call this class from trigger....? and this this is my class please send me how can i call this class from trigger..

public with sharing class casemerge{

public void mergecases(Case dupcase,Id mastercaseid){

System.debug('*************dupcase records**************'+dupcase);

//--------Duplicate all attachments

 List<Attachment> AttachmentsToBeCreated = new List<Attachment>();  

for (Attachment a : [SELECT Name, IsPrivate, Description, Body FROM Attachment WHERE ParentId = :dupCase.Id AND IsDeleted=false]){

 AttachmentsToBeCreated.add(new Attachment(ParentId = masterCaseId,Name = a.Name,IsPrivate = a.IsPrivate,Description = a.Description,Body = a.Body));        

}        

//-------Duplicate all comments

 List<CaseComment> CommentsToBeCreated = new List<CaseComment>();

 for (CaseComment cc : [SELECT IsPublished, CreatedDate, CommentBody FROM CaseComment WHERE ParentId = :dupCase.Id AND IsDeleted=false]) {

 CommentsToBeCreated.add(new CaseComment(ParentId = masterCaseId,IsPublished = cc.IsPublished,CommentBody = 'This case comment was originally created on ' + cc.CreatedDate +' and was merged into this case.\r\r' + cc.CommentBody));        

}

 if (!CommentsToBeCreated.IsEmpty())

 insert CommentsToBeCreated;

//-------Change the whatid for all tasks

List<Task> allTasks = [SELECT Id, WhatId FROM Task WHERE WhatId = :dupCase.Id AND IsDeleted=false];

if (!allTasks.isEmpty()) {    

for (integer i = 0; i < allTasks.size(); i++)    

allTasks[i].WhatId = masterCaseId;    

update allTasks;        

}

//-----Change the whatid for all Events

List<Event> allEvents = [SELECT Id, WhatId FROM Event WHERE WhatId = :dupCase.Id AND IsDeleted=false];

if (!allEvents.isEmpty()) {

for (integer i = 0; i < allEvents.size(); i++)

allEvents[i].WhatId = masterCaseId;            

update allEvents;        

}      

// duplicate all the attachments (of the case and related emails)

if (!AttachmentsToBeCreated.IsEmpty())

insert AttachmentsToBeCreated;  

// delete the original case and all it's related items

delete dupCase;

}

}