avrdude: ser_open(): can't open device "\\.\COM5" Sparkfun Pro Micro


I have some issue with the upload of sketch on a sparkfun pro micro board with the processor ATMega32U4 (3.3V, 8MHz).

It seems that my board is/was bricked. Actually, i'm able to upload a sketch but it needs ugly bootloader mode. The working sequence I am using now is :

State = COM6 on device manager & COM6 selected on Tool>Port

Double hit reset button : Bootloader mode activation
State = COM5 on device manager & COM6 selected on Tool>Port

Upload Sketch
Double hit reset button : Keep bootloader mode activation
Wait for Found Upload port COM5

Keep double hitting on reset button while the sketch is uploading (sometimes I double hit 3 or 4 times before the sketch is uploaded)

If i have the good timing (if I don't double hit when the sketch uploads) the upload works. Otherwise I have a "can't open device COM5" because of the double hits.

By the way, sometimes when I reactivate bootloader mode, the board doesn't start correctly and is no longer known by my PC which cause the failure of my sequence.

Maybe it helps to enable verbose output during upload in preferences.

For a Leonardo it shows the process and you can see when it tries to establish the connection (switching from COM6); that would be the moment to press the reset button. I don't have a pro Micro but it should be very similar.; in your case double tap, I guess.