Going crazy with arduino mini pro programmed by usb2serial

hi guys,
time ago I bought three arudinos pro mini
one to play with my sketchs and the other two to use on my finished projects.
now I have finished one project and I whant to program one of the two arduino pro mini

and here we are the trouble:
arduino ide don't program the board and give me this error: avrdude: stk500_getsync(): not in sync: resp=0x00

so I supposed to my usb2serial error but when I tryed to program the first arduino pro every thing goes all right
can any one tell me something to do for programing theese other two boards?? :cold_sweat:

I also have had this problem today with arduino mini pro boards (5 volt versions) connected to the IDE/PC via a usb2serial. The error is ".....not in sync...." and the sketch does not download. This indicates a failure in serial data transmission between the mini pro and the IDE/PC.
My usb2serial converter has a PL-2303 chip and I have four connections between the mini pro and the usb2serial as follows: VCC to 5 Volt, Ground to Ground, Txd to Rxd, Rxd to Txd.
The problem is that the mini pro must have a reset when the IDE commences the download sequence.
I have achieved successful downloads by pressing the mini pro reset button just after the TX LED first starts to flash on the usb2serial converter after the sketch is compiled and just as the download starts.