The project folder has red forks, and the rest of them are normal.

Generally appear in the project from elsewhere to check out or import imports, only the project folder has a red fork, other places are normal, now summarizes the individual's several solutions:

There are several possibilities:
1, the encoding settings are consistent, that is, your project's original encoding and now eclipse with the default encoding is consistent
2, the jar path in the import project may have been changed, in most cases this is the cause, and I have met, you have to make sure that your jar package path is not a problem. MyEclipse have a view of the jar path you can switch to see, the red X is the path has been changed, re-add in OK.
3, the problem console has the following error message:Java compiler level does notmatch the version of the installed Java Projectfacet. This can typically be done right--->properties--> the project and then find the project facets and Javacompiler two options to modify the JDK version that they use.

The project folder has red forks, and the rest of them are normal.