Scanner problem with W98

We are having problems with W98 randomly “losing” a scanner. The scanner is a USB connected Fujitsu fi-4220C. PC is P11, W98. After random number of scans, PC loses TWAIN driver. We unplug USB and plug back in. Reinstall driver, then scanner works again. We have also tried SCSI connection w/same problem. We have tried lower version of TWAIN from Fujitsu’s site to no avail. Does anyone have any ides???