Il problema nasce poichè ajaxcontroltoolkit non riconosce il browser impedendo ai updatepanel di fare CrossPostBack.
Per risolvere questo problema, in attesa di aggiornare i server al framework 4.5 ho trovato una scorciatoia.
Basta aggiungere al nostro progetto un file BrowserFile.browser ed aggiungere il seguente codice:
<browsers>
<browser id="IE11Preview" parentID="Mozilla"> <identification> <userAgent match="Trident/(?'layoutVersion'\d+).*rv:(?'revision'(?'major'\d+)(\.(?'minor'\d+)?))" /> <userAgent nonMatch="MSIE" /> </identification> <capabilities> <capability name="browser" value="IE" /> <capability name="layoutEngine" value="Trident" /> <capability name="layoutEngineVersion" value="${layoutVersion}" /> <capability name="isColor" value="true" /> <capability name="screenBitDepth" value="8" /> <capability name="ecmascriptversion" value="3.0" /> <capability name="jscriptversion" value="6.0" /> <capability name="javascript" value="true" /> <capability name="javascriptversion" value="1.5" /> <capability name="w3cdomversion" value="1.0" /> <capability name="ExchangeOmaSupported" value="true" /> <capability name="activexcontrols" value="true" /> <capability name="backgroundsounds" value="true" /> <capability name="cookies" value="true" /> <capability name="frames" value="true" /> <capability name="javaapplets" value="true" /> <capability name="supportsCallback" value="true" /> <capability name="supportsFileUpload" value="true" /> <capability name="supportsMultilineTextBoxDisplay" value="true" /> <capability name="supportsMaintainScrollPositionOnPostback" value="true" /> <capability name="supportsVCard" value="true" /> <capability name="supportsXmlHttp" value="true" /> <capability name="tables" value="true" /> <capability name="supportsAccessKeyAttribute" value="true" /> <capability name="tagwriter" value="System.Web.UI.HtmlTextWriter" /> <capability name="vbscript" value="true" /> <capability name="revmajor" value="${major}" /> <capability name="revminor" value="${minor}" /> </capabilities> </browser> </browsers>
Copiamo il file compilato sul server e tutto ritornerà a funzionare.