HP Officejet fax problem on SBS 2003

I’ve just installed a SBS2003. One client computer has a HP Officejet 7310 All-in-one printer/fax/scanner connected locally via usb. The printer works ok but the fax gives the error message ‘Fax cannot be sent due to a system error’. However, if I give the user admin rights, it works ok. HP says I must give admin rights for it to work. I don’t believe them. Any ideas?