No se genera el fichero .jar de mi programa

Buenas, tras terminar de hacer el programa, le di a limpiar y contruir para tener el ejecutable (utilizo el NetBeans IDE 6.1) y me salió este mensaje de error en el output y no se que tengo que hacer ahora, si me pudieras decir que significa...
init:
deps-clean:
Deleting directory D:\Documentos\Universidad\UNED\Programación III\Nonograma\build
clean:
init:
deps-jar:
Created dir: D:\Documentos\Universidad\UNED\Programación III\Nonograma\build\classes
Compiling 6 source files to D:\Documentos\Universidad\UNED\Programación III\Nonograma\build\classes
javac: invalid target release: 1.6
Usage: javac <options> <source files>
where possible options include:
-g Generate all debugging info
-g:none Generate no debugging info
-g:{lines,vars,source} Generate only some debugging info
-nowarn Generate no warnings
-verbose Output messages about what the compiler is doing
-deprecation Output source locations where deprecated APIs are used
-classpath
<path> Specify where to find user class files
-cp
<path> Specify where to find user class files
-sourcepath
<path> Specify where to find input source files
-bootclasspath
<path> Override location of bootstrap class files
-extdirs <dirs> Override location of installed extensions
-endorseddirs <dirs> Override location of endorsed standards path
-d <directory> Specify where to place generated class files
-encoding <encoding> Specify character encoding used by source files
-source <release> Provide source compatibility with specified release
-target <release> Generate class files for specific VM version
-version Version information
-help Print a synopsis of standard options
-X Print a synopsis of nonstandard options
-J<flag> Pass <flag> directly to the runtime system
BUILD FAILED (total time: 0 seconds)
muchas gracias!!