Eclipse 3.5 + ADT: build path errors

I am using Eclipse 3.5 for Jave EE Developers. Plugins installed include: Android Development Tools, Adobe Flash Builder 4, PDT, PyDev. I have problem with running the application I built.

I can start a new project, add a button, and run it on an 开发者_Python百科AVD. Then I add another button, try to run it on AVD, and Eclipse says 1) gen folder is missing, 2) there are errors with build path.

I can get ride of the first error by simply refreshing the project in the left pane, but the second error always sticks around. I searched online and on StackOverflow here and here, although several people have the same problem, there is no definite solution I can find.

Can somebody who fixed this problem successfully tell me how?

try this

a)Delete your project from Eclipse (i said ONLY from Eclipse, so uncheck option: Delete project contents on disk)

b) import your project to Eclipse: file > Import > Existing Projects into Workspace (Look for your project previously deleted from Eclipse) > Finish