Not Able to write in registry

It depends on the part of the registry you want to write to. You can write into HKey_Current_User.
When you want to write into HKey_Local_Machine, add a manifest to your application, stating requestedExecutionLevel level="requireAdministrator". See also http://msdn.microsoft.com/en-us/library/bb756929.aspx[^].
But think again whether it is really necessary to write data to that part of the registry. Often, a configuration file in %programdata%\Company Name\Product Name is more appriopriate.

Hello,

I use this before my methods to give that method proper permissions:

[System.Security.Permissions.SecurityPermission(System.Security.Permissions.SecurityAction.Demand)]

Hope this helps.