I have Eclipse Juno and Force.com IDE. When I try to create new classes they always show: failed to create the part's controls. It worked for the first time, but now they always show this. Same happens if I create them inside the force.com platform.
Error details:
org.eclipse.core.runtime.AssertionFailedException: assertion failed:
at org.eclipse.core.runtime.Assert.isTrue(Assert.java:110)
I had the same error. I fixed it by switching the eclipse workspace. Go to menu File->Switch Workspace->Other, and then select the same workspace you were working with. Eclipse will restart and you should not get the error.
