What are SQL Server Securables? I migrated two applications to the new server. One of the them works without any issues but the other ran into back end sql permission problems like 


  The EXECUTE permission was denied on the object
  ‘aspnet_CheckSchemaVersion’


I could find figure why one application would work and the other would not. They both run under the same application pool but uses different database. I didnont have to do anything for the one that to work, for the other I had to grant permission on [Network Service] user for each table, stored procedure which the application access.

Well I have resolved the problem now by making the two databases securables for Network Service. I dont know why I had to do this for one application while the other does not need it. My question is

What is SQL Server Securable in SQL Server Management Studio? You basically access them when you click on user -> Properties then go to second page on the left. 

What is it used for? What is its proper use?

From Microsoft


  Securables

Lists the securables on which specific permissions have been granted or denied to  this principal.
A securable is anything that can have permissions granted, denied, or revoked on in SQL Server.  It's basically "something you can secure".

Think about it like this:  Your car is a securable.  You would have to have been given keys (permissions) to access your car (securable).

A securable is anything that can be accessible or inaccessible.

Take a look at this BOL reference on Securables.  Under the three scopes of securables (server, database, schema) you can see a listing of the contained ones.  Here is the list of securables (taken directly from BOL, but for reference):


  Server Scope Securables
  
  
  Endpoint
  Login
  Database
  
  
  Database Scope Securables
  
  
  User
  Role
  Application role
  Assembly
  Message Type
  Route
  Service
  Remote Service Binding
  Fulltext Catalog
  Certificate
  Asymmetric Key
  Symmetric Key
  Contract
  Schema
  
  
  Schema Scope Securables
  
  
  Type
  XML Schema Collection
  Object
  
  Aggregate
  Function
  Procedure
  Queue
  Synonym
  Table
  View