When the number of work items in a TFS iteration exceeds 500, a red warning appears in the TFS Web page (Web Access) display the number of items in the backlog exceeds the configured limit of 500. The current total is 529 .....
TFS displays work items such as 500 requirements/tasks by default in the iteration view, beyond which a warning message (such as yours) appears, but does not affect the iteration view or the results of the query.
You can modify the limit number by reconfiguring the process profile for TFS by following these steps:
1. Open the command-line window and navigate to the installation location of Viusal Studio 2013
My computer is: C:\Program Files (x86) \microsoft Visual Studio 12.0
2. Export the process profile using the witadmin tool
witadmin exportprocessconfig/collection:collectionurl/p:projectname/f: "Directorypath/processconfiguration.xml"
3. Open the exported configuration file using any text editing tool (such as Notepad) and add the attribute workitemcountlimit to the Taskbacklog node, for example:
<taskbacklog category= "Microsoft.taskcategory" pluralname= "Tasks" singularname= "Task" workitemcountlimit= "800″ >
4. Using the WitAdmin tool to import the modified process configuration file
witadmin importprocessconfig/collection:collectionurl/p:projectname/f: "Directorypath/processconfiguration.xml"
Reference: http://blog.imaginet.com/change-the-work-item-limit-in-the-tfs-2013-sprint-backlog/
Modify the number of work items limit in the iteration view of TFS 2013