[PD] raspberry comport error 2

[rolfm at dds.nl]

hello,

Slowly trying to get a grip on RPi.

Pd & Arduino combo works on Windows 10 & OSX.

now on Raspberry Pi 3 Raspbian Jessie, Vanilla with pd-comport from 
repository.

Arduino IDE (older version) works allright on  Pi USB Serial connection.

Opening the port in Pd goes alright:

[comport] closed port 1 (/dev/ttyAMA0)
[comport] set_baudrate: Setting baud rate to 115200 with baudbits 0x1002
[comport] opened serial line device 1 (/dev/ttyAMA0)

Trying to send a byte from Pd to Arduino:

[comport]: Write failed for 0 bytes, error is 2

There seems to be no error-'guide' for comport.

What could be the reason?

rolf