Now it seems I can't load any class in [mxj]

Even the mxj.maxhelp can't load the help.class

The 1st message I get in Max window when I try to load a class is:

Could not load class 'com/cycling74/jitter/JitterObject'

For example the jitter.jar is in Cycling '74/java/lib

Java(TM) SE Runtime Environment (build 1.6.0_20-b02-279-10M3065)

Java HotSpot(TM) 64-Bit Server VM (build 16.3-b01-279, mixed mode)

MBP 2.93GHZ 4Go 1067MHz DDR3 9400M+9600MGT

I started with java a few week ago.
Now it seems I can't load any class in [mxj]
Even the mxj.maxhelp can't load the help.class

The 1st message I get in Max window when I try to load a class is:
Could not load class 'com/cycling74/jitter/JitterObject'

But the files are there!
For example the jitter.jar is in Cycling '74/java/lib 

java version "1.6.0_20"
Java(TM) SE Runtime Environment (build 1.6.0_20-b02-279-10M3065)
Java HotSpot(TM) 64-Bit Server VM (build 16.3-b01-279, mixed mode)

MBP 2.93GHZ 4Go 1067MHz DDR3 9400M+9600MGT
MaxMSPJitter 5.1.5

cant-load-any-mxj

Don't know if it help but: Last time i had the same kind of problem, i just reinstalled max and it worked again.

can't load any [mxj]