Error - Operation is not valid due to the current state of the object.

Whenever a postback is done, this error occurs when form fields are very large in number. The stack trace is:

at System.Web.HttpValueCollection.ThrowIfMaxHttpCollectionKeysExceeded() at System.Web.HttpValueCollection.FillFromEncodedBytes(Byte[] bytes, Encoding encoding) at System.Web.HttpRequest.FillInFormCollection()

By default, the maximum value of MaxHttpCollection is 1000.
To solve this error, increase the MaxHttpCollection value. Try adding the following setting in your web.config's <appsettings> block.

<appSettings>
      <add key="aspnet:MaxHttpCollectionKeys" value="2001" />  
</appSettings>

It can solve your problem. If you have very large records on your page, say 600 records in a grid, and you click on Submit, then increase the value of MaxHttpCollection.
Then change value 2000 to 5000 and test again. It will be resolved. :-)

-->