Windows XP Networking Problem

On a small network(Win98 & XP) I have shared several folders on the XP PC. These folders hold Quickbooks and Shopkey databases. From a 98 PC (which has the shares mapped and is logged on as an admin-equivalent user) when the shopkey data is accessedalone every thing is OK. When Quickbooks is run at the same time, it can not access any shares from the XP PC. Does any one know of any XP networking issues that would cause this to occur?