The default setup for the D$ shares is for machine administrators. If the user account that SSRS is running under is not an administrator it will not be able to write to the share.
By using \localhost\D$ it is accessing the local D drive. It should work by just specifying D:\PrimeCare\import\sprinkle. Other users can then access the location with \{servername}\d$\PrimeCare\import\sprinkle