There was an error processing the request

If you get that above error.. and you have no idea what's wrong with it just put change "CustomError='Off'"

WebForm_... is not Defined error

If you get this error "WebForm_ is not defined error..."
and previously you never get this problem...

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you may install a plugin which compress the .axd file...

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solution:
you need to exclude them on the compression module...
please check your .axd name.. and exclude them on your HTTP compression module


it needs this 2 file not to be compressed
System.Web.Script.Services.ScriptHandlerFactory, System.Web.Extensions

and

System.Web.Handlers.ScriptResourceHandler, System.Web.Extensions

Protect yourself from XSS attack with new ASP 4.0 nuggets

In ASP.NET 4.0, you can replace your usually habit to use <%=%> with this new nuggets <%: %>
This will automatically protect your applications against cross-site script injection (XSS) and HTML injection attacks and avoid duplicate encoding.

So you don't need to worry if you forget to encode your string in the aspx files. or protect it using AntiXSS.

It's very usefull in combination of MVC framework 2.0