Solution for Eclipse Error:"Couldn't find a client to launch the selection."

When to run a selected Dynamic web project in Eclipse WTP3.2,Error "Couldn't find a client to launch the selection." may be reported by Eclipse. Google the error, some ones say that this is a bug of WTP, the solution given is, "Close your web browser which is used for the project." But I find the solution is ineffective at most of times. By try many times, I found a solution for the error,

1. Delete project from eclipse, but not delete source.
   
2. Delete .classpath, .project, and .setting from the folder of the project.
   
3. New a project in the original folder. If the folder's name is prjOne, new a project named prjOne under this folder.
4. Close your web browser selected to run the project before to run the project. This is recommended.