By default, web.config of SharePoint (should be there: C:InetpubwwwrootwssVirtualDirectories80) defines the maximum number of controls as 200. Should you define more on a page you’ll probably get an error similar to this:
In order to fix it, edit this web.config. Find configurationSharePointSafeMode tag and change the MaxControls attribute to a bigger number. Once you do this, reload the page. It should help.