I've had a similar issue with sharing when the accounts have no password/blank password.
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		| k, well xp pro has a 'feature' they call it that does not allow blank passwords.  To turn this off go to the xp machine -> start -> control panel -> administrative tools -> local security policy -> local policies -> security options -> "Accounts: limit local account use of blank passwords to console login only".  Change the value to disabled. | 
	
 quoted from this page which may also give you ideas for fixes 
http://www.experts-exchange.com/Netw..._21052862.html