In SharePoint 2010 if CMSSiteManager.js library is loaded besides jQuery, then much of stuff stops working. The reason is that the dollar sign ($) is used in cmssitemanager.js as well which conflicts with jQuery. Mostly it appears on pages where you load jQuery and have an image library with thumbnails. To avoid this, just replace all $ with jQuery in your custom scripts. A more crazy situation is when avoiding $ isn’t enough. It is when you load jQuery to page head automatically on all pages. The Asset picker (AssetPortalBrowser.aspx) invokes $ itself and gets with jQuery in conflict without you write a single line of custom javascript code. You usually get the following error: