Heya, a few things you can get them to try...
Firstly, make sure they have the latest drivers from
http://www.motorola.com/networking/products/sm56_pci_software_modem/drivers.html Secondly, under Network settings for the Dialup connection properties, click the settings button and make sure Enable LCP extensions & negotiate mutil-link for single link connections is OFF.
Had a buddy with the same prob a few months back, and that's what we did to fix his.
Good luck
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Intel PIII 450
ASUS P2B-F (BIOS 1013)
128 MB PC 100 SDRam
Diamond Viper 770 32Mb TNT2 (Det. 5.32)
Quantum Fireball CR 8.4Gb IDE HDD
Quantum Atlas II 4.5Gb SCSI HDD
Tekram DC-310 SCSI Adapter
Panasonic CW-7502 8x4 SCSI CD-R
Mitsubishi Diamond Data 32x IDE CD Rom
Creative Sound Blaster PCI 64 (ES 1370)
Logitech Wingman Extreme Digital 3D USB Joystick
Epson Stylus Color 400 Printer
Dynalink V1456VQE-R External 56k V.90 Modem
Daewoo 710b 17" Monitor
Windows 2000 2195
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#NTCompatible on UNDERNET!!!