I am using freeRtos to handle some task.. I've added 4 task where one of the isn't running. (used for debug purpose, but it should be runnning)

when I add another task to my scheduler, crashes freeRtos, and nothing run.. Have i reach some kind of limit or how come doesn't freeRtos run any task on my µc???

There are lots of possible reasons including a mistake in your code, a linker script error, a configuration error, and so on.

Do you have a debugger attached? If so look at the return values when you call xTaskCreate(), and where the program counter is when it crashes (maybe its just in an assert() call?). Do you have a malloc failed hook defined [http://www.freertos.org/a00016.html]? Do you have a stack overflow hook defined [http://www.freertos.org/Stacks-and-stack-overflow-checking.html]?

Does shared FreeRtos queues need mutex lock or are the included in the queue??? Cause..it doesn't crash when I remove one of the task that shares a queue with,

Queues are part of FreeRTOS, and as such are thread safe, so you do not need to use your own mutex lock.

Maybe if you posted the code we could see what was wrong.

Regards.