If you use full-text searching, you must grant the NT Authority\System sysadmin rights to SQL Server if the Builtin/Administrators role is removed:

EXEC sp_grantlogin [NT Authority\System]

EXEC sp_addsrvrolemember @loginame = [NT Authority\System], @rolename =  'sysadmin'

See http://support.microsoft.com/?id=263712 for the full article.