"setPin: Protocol error" and "setPin: Value too large for defined data type" error

[domingok]

I'm using SvxLink on a Raspberry Pi Zero 2W.
I manage the PTT with an interface made for other similar software (e.g. Echolink).
This interface uses a CH104 chip for USB <--> Serial conversion.
Normally it works well, but when the PTT signals are short and close together, the radio's PTT (managed via the RTS pin of the serial port) gets stuck in TX.
In svxlink.log i see the message "setPin: Protocol error"
or sometimes "setPin: Value too large for defined data type" error.

Any suggestions?

Many thanks in advance
Domingo IZ7OIX