Access Network File Sharing Problem

I am running a small access database over a wireless network which all worked fine (still does on 1 wired/3 wireless) with not too many problems total of 6 machines (5 wireless/1 wired). I have just replaced two machine as they were getting a bit old 3years. But these two new machines do not seem to have full rights to the access database, in that I can open the database and view records but when you add data you get a Disk Error message. I can open and share word documents etc but not the database – if I reverse this set-up I get the same problem the wired computer can open and save word documents but again not the database - what am I missing!!!

SET-UP = All machines have Windows XP Pro and Office 2003 with all windows/office updates done, all connected to the same workgroup etc. Two new machines are Dell with Dell Wireless adapter. No server just workgroup and database in a shared folder on one computer which is hard wired to the Netgear wireless router. I have not run any network wizards and I don’t think I need to, just sharing the folder should be enough? Windows is managing the dell wireless adapters, file and print sharing is enabled, other computers can print to this computer, but I just can’t get the database to share correctly – I have also checked “References” and all looks fine.