How to use button to mass/bulk update field values in picklists

How to use button to mass/bulk update field values in picklists

Hello, I want to create a button with a function that will mass/bulk update field values in picklists. 

So I created this function… 
  1. mp = Map();
  2. mp.put("Name_Of_Picklist1","NEWVALUE1");
  3. mp.put("Name_Of_Picklist2","NEWVALUE2");
    4. update = zoho.crm.updateRecord("Contacts",contactID,mp);
  4. info update;
  5. return "";

This works fine when I select 1 record in the list (module "Contacts"). But when I select 5 records and press the button there is an error message. 

How can I solve this?

Thanks for help, 
M.