ok, I found the problem.
The TIMER4 pin multiplex configuration must be set to (IEN | MODE2). I thougth this was the default setting for TIMER4 pin at board startup, but it seems that it was not the case 
kudos to me 
ok, I found the problem.
The TIMER4 pin multiplex configuration must be set to (IEN | MODE2). I thougth this was the default setting for TIMER4 pin at board startup, but it seems that it was not the case
kudos to me