I've seen many users on the mailing lists or in my company who get this error message:
Cannot execute mojo: resources. It requires a project with an existing pom.xml, but the build is not using one.
Most often than not they do not understand what the cause of the problem is.
Most often that not this is simply because they are 1 directory up or down relatively to the directory that contains the pom.xml of the project they want to build.
I suggest that the error message should be updated to something like:
Cannot execute mojo "bla". Maven was executed in directory "foo" and it doesn't contain a pom.xml
Moreover, maven should look 1 directory up and 1 directory down from the basedir for pom.xml files. And if one is detected suggest the user to move to that directory.