I have just tested the board with SIM900 librairy . I was using exemple GPRS_send SMS with Pin TX8 and PinRX 7 it work perfectly at the first time , i have received SMS on my phone and friend’s phone. After one day I try again but i forgot to reverse pin 8 and 7 into the sketch and nothing happen so i have seen my mistake and have reverse the 2 pins. Apparently too late 
Now I get the message init error each time. I am afraid that CPU or SIM 800 has a pin destroyed
When you put 2 output together it coudl be bad ! I would like to know if any body has some experience with the same error ? thanks you
Sory but in fact the board is running well 
. I test it with the SIM800 library and it is OK. One thing curious , the SIM900 library doestnot work since my mistake and so i have some difficulties to connect with Ubidots.
I have try GPRSBee library without succes. If somebody has a good skech for Ubidots i will be happy.