I am a CS student learning Java so I do some work at home and at college on a mixture of Linux and Windows. I have a problem after copying a new project into the Eclipse workspace. The project shows up but with a red exclamation mark and an error saying:
The project cannot be built until build path errors are resolved
"project navigator" or
"package explorer" view.
Right click on your project, select
Build Path --> Configure build Path.
In the emerging window, you will find four tabs, select
"Web app libraries" (expand it), you will see the libraries added to the project's classpath. Check if all of them are available. If one or more are not (they'll have "missing" beside their name and a red mark on their icon), check if you need them (perhaps you don't); if you don't need them, remove it, if you need them, exit this window, look out for the missing jar and IMPORT it into your project.