From the forums:
"This file seems to be a driver for a US Robotics Sportster ISDN 128k modem and is on the Windows98 CD.
To get rid of the message one of the following will work:
1. From start-->run type: sysedit
Close each window until you are looking at system.ini
Scroll down to the [386enh] section and see if you have a line that reads something like:
Device=C:\Windows\System\Sibbri.386
If you do, edit the line to put the letters REM and a space in front of the text so it now reads:
REM Device=C:\Windows\System\Sibbri.386
From the File menu, save the file then exit sysedit. Reboot and the message will be gone.
2. From start-->run type: regedit
From the Edit menu, click Find and search for sibbri.386 in values & data.
When you find the name key with this value you can delete it.
Press F3 to repeat the search in case it appears again.
Reboot"