Some weeks ago a teammate went to my office asking for help to troubleshoot a weird behavior on a web application. The symptom was that one but only one existing form in the application stopped raising events. At that point the only clue we had was the date it stopped working.
I made a quick check and I figured out that the form had the form action attribute defined on the html and it was pointing to a different page than it should be. Ok but it did not make any sense because the .NET web form does not use this attribute. So I checked if something had changed on the server and voilà. Exactly on the same date when the application stopped working the .NET 3.5 service pack 1 was installed. Mystery solved. This is a known issue for the SP1 install because starting on this version the form action attribute starts to be valid again. Below is a list of the most common issues related to the content of the .NET 3.5 SP1 that may break some existing code.
Issue: Html form action attribute is now used by the runtime.
Workaround: Remove the action attribute from the html.
Issue: App_browser hidden content is not ignored.
Workaround: Simply delete them.
Issue: System.Web.UI.WebControls.EntityDataSourceWrapper does not contain a property with the name… error message during compiling.
Issue: Make sure that the class defined in this code file matches the ‘inherits’ attribute error message is generated when using pageBaseType attribute in web.config.
Workaround 1: Remove from the web.config if it’s not needed for all pages;
Workaround 2: Change the inheritance from System.Web.UI.Page to your base page type.