Microsoft has documented occurrences of a problem with the default Network Adapter Driver that comes with Windows 98. According to the Microsoft Knowledgebase article
(at support.microsoft.com/support/kb/articles/a189/7/78.asp, article #Q189778) the default Realtek network adapter driver may send an occasional corrupt data packet. This has caused known data corruption problems with several First Resort clients.

To check if this could be a problem on your Windows 98 workstations, right click on the 'my computer' icon from your desktop. Select 'Properties' and then select the 'Device Manager' tab. Double-click the 'Network Adapters' icon and right click on the 'Realteck Network Adapter' (if present), then select 'Properties.' The problem can occur if you are using the RTL8029.SYS driver.

To resolve this problem, download and install an updated driver from the Realtek web site: www.realtek.com.tw/cn/driver/8029-driver.htm.