Actually, the scala script for execution contains a non-standard option -Xbootclasspath/a:path. Then, when executing scala script, if you decide to precise a special java virtual machine that does not implement this non-standard option, you will get this error:

** ERROR: unrecognized option '-Xbootclasspath/a:/home/username/scala/lib/jline.jar:/home/username/scala/lib/scala-compiler.jar:/home/username/scala/lib/scala-dbc.jar:/home/username/scala/lib/scala-library.jar:/home/username/scala/lib/scalap.jar:/home/username/scala/lib/scala-swing.jar

For example, in my case, it was with the real time java virtual machine called JamaicaVM which does not support this option.
My solution was to replace -Xbootclasspath/a:path by -Xbootclasspath:path and to add the current directory "." at the bootstrap classpath.