How to figure out why I'm getting “HttpCompileException was unhandled by user code”?

Question

I am brand new to SharePoint, SharePoint development, and MS development.

My SharePoint dev environment consists of Windows 2008, SharePoint 2010, and Visual Studio 2010.

I created a very simple "Hello World" Visual WebPart, deployed it to SharePoint through Visual Studio, added it to a new page, and was able to view it with no problem.

I then enhanced the WebPart by adding a few controls and some code. When I deployed the Web Part, and went to the page containing it, I received an error in Visual Studio: "HttpCompileException was unhandled by user code".

I then erased all of my new code, so that the XXXUserControl.ascx file contains only a single button and the XXXUserControl.ascx.cs file contains only an empty Page_Load method. I deployed again, but received the same error.

I'm looking either for an explanation of what's happening, or tips on how to debug.

Details:

The error is: "HttpCompileException was unhandled by user code"

The error occurs in the auto-generated XXXWebPart.cs file on the line marked with "<-----" below:

namespace UserSyncTest1.UserSyncTest1WebPart
{
    [ToolboxItemAttribute(false)]
    public class UserSyncTest1WebPart : WebPart
    {
        // Visual Studio might automatically update this path when you change the Visual Web Part project item.
        private const string _ascxPath = @"~/_CONTROLTEMPLATES/UserSyncTest1/UserSyncTest1WebPart/UserSyncTest1WebPartUserControl.ascx";

        protected override void CreateChildControls()
        {
            Control control = Page.LoadControl(_ascxPath);  <-----
            Controls.Add(control);
        }
    }
}

The output window contains:

A first chance exception of type 'System.Web.HttpCompileException' occurred in System.Web.dll

Answer 1

The error can relate to a lot of things:

File (ASCX) is not valid: Create

• a new visual webpart, then compare the 2 ascx files, a small typo like a < or > to much can break a file
• Did you change any project settings: Target framework (can't be 4.0), Deployment type (Sandbox or Farm)
• Server ran out of memory and stopped compiling (Check the eventlogs)
• SharePoint is "broken" i.e. SharePoint's Virtual Path Provider is looking for the ascx in the wrong place: delete webapp, reboot, then recreate webapp + sitecollection and redeploy

Answer 2

In UserCode solution type, you can't refer to the disk (in this case, the LoadControl will have an IO on the server, to the file /_CONTROLTEMPLATES/UserSyncTest1/UserSyncTest1WebPart/UserSyncTest1WebPartUserControl.ascx).

You should, or make a Farm Solution, or generate your HTML from your control, in code, not in declarative way.