Hi Paul;
Problem solved!
I had misswired the FT232RL USB adaptor to the Arduino Pro Mini.
The correct wiring is:
Connect wire ( jumper) from FT232RL 3.3V to Arduino VCC
from FT232RL GND to Arduino BLK
from FT232RL TXD to Arduino RXI
from FT232RL RXD to Arduino TXO
from FT232RL DTR to Arduino GRN
Do not connect VBUS
Regards
Pierre Salsiccia