Operation is not valid due to the current state of the object. when i select dropdown list [duplicate]

Answer 1

From http://codecorner.galanter.net/2012/06/04/solution-for-operation-is-not-valid-due-to-the-current-state-of-the-object-error/

Issue happens because Microsoft Security Update MS11-100 limits number of keys in Forms collection during HTTP POST request. To alleviate this problem you need to increase that number.

This can be done in your application Web.Config in the section (create the section directly under if it doesn’t exist). Add 2 lines similar to the lines below to the section:

The above example set the limit to 2000 keys. This will lift the limitation and the error should go away.