Environment Varables > Classpath
This environement variable is case sensitive. It is CLASSPATH, not Classpath.
Eclipse complains that It can't resolve it.
I don't think that Eclipse uses the Windows CLASSPATH variable. Right-click your project, click "Properties". Go to "
Java Build Path/Libraries", click "Add external class folder". Select "C:\JavaCode\ReusableClasses" and click ok.
(If you really want them to be reusable, I think it would be better to package them in a JAR file)