Custom Activities not showing up in VS2012

This issue was driving me crazy for couple of months. I had to explicitly add my assemblies to the toolbox every time I added or removed custom activities in my project. I googled it and found a few posting with similar problems but no one seems to have found a solution. After some tweaking I was able to fix it by narrowing it down to a single project in my solution that caused custom activities not showing up in the toolbox even for those custom activities defined in a different project belonging to the same solution. It turns out that the "$(SolutionDir) in the .csproj was set to wrong relative path. I think I have been moving the project around from one folder to folder before I was finally happy with its location. To investigate this, I removed the project from the solution, and created another one at the same folder hierarchy relative to the solution folder and then added the new project to the solution and then compared the .csproj files between the new and bad project. This is how I found that the "$(SolutionDir) was messed up in the bad .csproj file. Regardless, shouldn't it have been updated automatically? I went from this: ..\..\..\ To this : ..\ And now all my custom activities show up. To make sure this is the cause I reverted the change and I got the toolbox not refreshing problem again.