by Ron Grzywacz (http://forums.microsoft.com/technet/showpost.aspx?postid=1130848&siteid=…)
Ensure your permissions are set as noted below. Then try to restart the service from central admin.
Fixing Search Propagation share issues
In the Query Server Index File Location section, select one the following:
• Configure share automatically
Select this option to automatically configure the share on which you want to store the propagated index. Type the user name and password of the account that you want to use to propagate the index. (Recommended)
This account must a member of the Administrators group and a member of the WSS_ADM_WPG group on the query server before you proceed to the next step or propagation of the index will fail.