Unknown error in Android project

Possible
Duplicate:
href="https://stackoverflow.com/questions/2194808/debug-certificate-expired-error-in-eclipse-android-plugins">“Debug
certificate expired” error in eclipse android plugins

As
you can see from my profile, I have programmed lots of Android projects already.
However, I am now stuck, maybe due to the new Eclipse plugin or SDK
version.

I created a new project for Android 1.6
and SDK 4. Once, I compile the build as it is, I see an error mark (X) in the project
top element. However, there is neither a description, nor a quick fix available, and
none of the project files display an error mark. I cannot run the
project.

What is going on? How can I get any
information about that
error?

Thanks.