I've seen posts about this error 852 "Can not write to the external storage", I currently have this problem when we setup a Server 2016 the network is running Active Directory also and running FMS 16 in VM.
Clients are running FMPA15, FM Go all get this "Can not write to the external storage" when adding images to the DB.
Storage is set to external and no secure is not checked
I can not do drag and drop into the field I get "Can not write to the external storage".
I can not do a picture from FM Go via the add image by camera.
If I add a picture via the insert picture on the layout and I check the Store only a reference to the file it will work.
I have seen some say that mapping a drive will help others say reinstall Filemaker Server (have to get IT to do that).
We have been waiting over a year to get this in place to use, ( I actually went out on a limb and got my boss on board for us to use Filemaker products).
Does anyone have any suggestions for what I should do.