NetBeans 4.0 does not have built-in support for
SCCS.  This is fine, but it should at least be
able to co-exist peacefully with SCCS.  Currently,
it does not.
The usual way to use SCCS is to create a
subdirectory called "SCCS" in every source
directory.  SCCS will put two kinds of files in
this subdirectory.  For a source file like
Thing.java, it will store the different versions
in a readonly file called "SCCS/s.Thing.java".
When the file is being edited, it will store
the version being edited in a writeable file
called "SCCS/p.Thing.java".  The problem is
that when NetBeans goes looking for Java
source files, it finds this SCCS/p.Thing.java
and inserts a package declaration in it!
So for example, in the package
com.example.whatsit, NetBeans will find the
file com/example/whatsit/SCCS/p.Thing.java
and insert a package declaration into it:
package com.example.whatsit.SCCS;

You can still use SCCS after this change, but
you will get warnings from it because it will
consider that the package declaration means
that some other version of the file is being
edited.

Without requiring NetBeans to have any hacky
special knowledge of SCCS, like avoiding
subdirectories called "SCCS", it could simply
consider that a file that has two dots in its
name (like p.Thing.java) cannot be a Java
source file, and ignore it.