[решено]при подкл. ppp Couldn't attach tty to PPP unit 0: Invalid argument

при попытке подключения по gprs:
gamma linux # pppd call gprs-moto-usb
GPRS modem init: press -C to disconnect
+ defining PDP context
+ defining QoS requirements
+ attaching to GPRS
+ requesting data connection
Serial connection established.
Couldn't attach tty to PPP unit 0: Invalid argument

Использую motorola c 380 usb
Ядро собрано с:
[*] PPP filtering
{M} PPP support for async serial ports
{ } PPP support for sync tty ports
{M} PPP Deflate compression
{M} PPP BSD-Compress compression
{M} USB Modem (CDC ACM) support

gamma linux # ls /dev/ | grep ACM
ttyACM0

# $Id: gprs-moto,v 1.1 2001/12/10 16:17:15 tjd21 Exp $

name beeline
/dev/ttyACM0
#/dev/usb/acm/0

# Serial port line speed and options
57600

# Control character handling
asyncmap 20A0000
escape FF

# Generic GPRS options
file /etc/ppp/gprs-options

подскжите, пожалуйста, в чем возможная причина неисправности.
Обновил ppp, включил MPPP, PPP sync