Error when populating sharePoint 2010 Web Part Gallery

when you try to populate share point 2010 web Part Gallery an error page ( yellow page) shown

Going to Event Log show this info:


Event code: 3005
Event message: An unhandled exception has occurred.
Event time: 3/23/2013 8:25:30 AM
Event time (UTC): 3/23/2013 5:25:30 AM
Event ID: 61c57a10998343b6ba69332e97299559
Event sequence: 9779
Event occurrence: 24
Event detail code: 0

Application information:
    Application domain: /LM/W3SVC/828672489/ROOT-1-130084692648142416
    Trust level: Full
    Application Virtual Path: /
    Application Path: C:\inetpub\wwwroot\wss\VirtualDirectories\80\
    Machine name: .........

Process information:
    Process ID: 12572
    Process name: w3wp.exe
    Account name: .....

Exception information:
    Exception type: InvalidOperationException
    Exception message: Operation is not valid due to the current state of the object.

Request information:
    Request URL: http://xxx/_layouts/newdwp.aspx
    Request path: /_layouts/newdwp.aspx
    User host address: 87.101.230.49
    User: .....
    Is authenticated: True
    Authentication Type: Federation
    Thread account name: ......

Thread information:
    Thread ID: 21
    Thread account name: ......
    Is impersonating: False
    Stack trace:    at System.Web.HttpValueCollection.ThrowIfMaxHttpCollectionKeysExceeded()
   at System.Web.HttpValueCollection.FillFromEncodedBytes(Byte[] bytes, Encoding encoding)
   at System.Web.HttpRequest.FillInFormCollection()

To solve this problem  add the following to your web.config for your IIS web application:

<appSettings><add key=”aspnet:MaxHttpCollectionKeys” value=”2000″ /></appSettings>

where 2000 is any value the meet your need.