A project with output type of class library cannot be started directly - with a startup exe

Question

Firstly I'm completely aware of this message and why it happens normally. It's not that I'm just trying to run a dll (like this question).

I have a project that compiles to a dll but has a startup program specified in the project properties. Most of the time I'm able to right-click on the project and select Debug > Start new instance, and it will run the program and let me debug my dll. However, occasionally I get this message (A project with output type of class library cannot be started directly) as if I haven't got a startup program. The first few times I thought it was just me accidentally clicking on the wrong project but I'm certain this isn't the case given that it's happened so many times and I've been careful to watch it.

When this message appears I'm able to try it again and it always works on the second or third attempt.

A colleague using the same Solution never has this problem :-/

Anyone else had this problem or know how to solve it?

I'm using Visual Studio 2005 Pro Version 8.0.50727.762 (SP.050727-7600)

Answer 1

This sounds like a transient Visual Studio problem. Reinstallation or upgrade may solve your problem.

Answer 2

Typically problems in VS are caused by:

• Add-ins: Run VS without and see if the problems is solved
• Corrupted files in your solution: Delete / rename all files created by Visual Studio which are not part of your project, i.e. all .suo, .ncb files and a like.

Answer 3

I had this problem with projects that were created as "Windows Control Library" that somehow forget their status. Unloading and reloading the project usually did the trick.

If it was created as a "Class Library" then to make it a "Windows Control Library" I manually add the following to the .csproj file. It was the only difference I could see between a class library and windows control library project.

BTW - starting a Windows Control Library starts the User Control Test Container - allows you to test any user control in the library. Very cool.

<Service Include="{94E38DFF-614B-4cbd-B67C-F211BB35CE8B}" />

add that inside of an <itemgroup> element.

Answer 4

no just make a start up project

Answer 5

Another colleague suggested it's because after clicking Debug > Start new instance, while I'm waiting for it to start up, I click on a different project. I don't do it for any reason, just randomly selecting things as I wait for the project to start up. Maybe Visual Studio looks at the selected project sometime after I clicked the menu, gets confused, and shows the error message?

Anyone able to confirm this matches their experience?