Eclipse Maven Import error: An internal error occurred during: Importing Maven projects. Unsupported IClasspathEntry kind=4

Problem
After using the command mvn eclipse:eclipse, the project is imported by Eclipse using the "Existing Maven Projects", which throws the error message:
An internal error occurred during: Importing Maven projects. Unsupported IClasspathEntry kind=4

Solution
Do not use the "mvn eclipse:eclipse" command.
Do a straight import by Eclipse using the "Existing Maven Projects".
An incompatibility is commented here.

TIP
About compatibilities between command line vs. Eclipse's maven plugin, when the "Run Maven Build" option (Shift+Alt+X M) doesn't work properly, use the command line as follows:

cd project_root (where pom.xml is)
mvn install -U

Return to Eclipse and refresh the project (F5 over project).