Cannot send fax

Hi,

I just bought a USB modem to send/receive fax.
I've installed fax service in XP.

However, I cannot send fax successfully every time.
When it failed, the error is "Line is busy".
Sometimes, the machine even hung up and need reboot.

If I can send fax sometimes, it seems that the setting is OK.
Is it the hardware problem?


Regards,


Johnny