I thought this particular issue warranted a blog post because it took me a good couple of hours to track down the problem. Essentially as the title suggests, my custom Workflow 4.0 activities were not appearing in the Workflow 4.0 toolbox on a few projects I am working on.
If I created a new Workflow 4.0 project in Visual Studio 2010, everything worked as it should. However, if I integrated Workflow 4.0 with an existing project I ran into problems. After numerous Google/Bing searches I found a few examples of forum/stackoverflow posts about the problem but usually in the VS2010 Beta context.
It tuned out that the problem in my case is that I had two projects in my solution where the project files (*.csproj) were in the same directory. VS2010 did not like that for some reason. After moving the two projects into separate folders, everything worked! Absolutely bizarre.
If you are interested, the reason I had two project files in a single directory was because it’s the default configuration when using LLBLGEN (adapter mode). It generates two projects, one database specific and the other generic. It is possible to get LLBLGEN to generate the projects in separate folders, you can find the instructions here.
Feel free to play the sad trombone if you wasted as much time as I did.