Uploading a file to a folder on a datastore using vSphere fails

Question

I am running vCenter 7.0 Update 3n with a half dozen hosts. I have a role set up that I called "Datastore Uploads" so that non-admin users can upload ISO's to a folder on an NetApp NFS datastore share that was created specifically for this purpose (called simply "User Share"). The users that need this upload capability are in a specific Active Directory group that I created. I created an "ISOs" folder on the datastore and then added the Active Directory group (called "vSphere Uploads") with the "Datastore Uploads" role to the permissions on the datastore. I assigned the "Datastore Uploads" role the following privileges:

• Allocate space
• Browse datastore
• Low level file operations
• Remove file
• Update virtual machine files
• Update virtual machine metadata

However, when users attempt to upload files to this folder, they get that annoying "The Operation Failed" error, with the details:

"The operation failed for an undetermined reason. Typically this problem occurs due to certificates that the browser does not trust. If you are using self-signed or custom certificates, open the URL below in a new browser tab and accept the certificate, then retry the operation.

https://myvcenter.com

If this does not resolve the problem, other possible solutions are shown in this KB article: http://kb.vmware.com/kb/2147256"

I tried the suggestions in http://kb.vmware.com/kb/2147256 but this did not help.

I have done search after search after search on this issue, and I know this question has been asked over and over again, but they all pretty much suggest the same solution in http://kb.vmware.com/kb/2147256, which is to go to the vSphere landing page then use the "Download trusted root CA certificates" link to download and install the trusted root certificates. I have installed the certificates in Windows as "Trusted Root Certification Authorities" for use with Chrome, and imported the certificates in Firefox under Authorities as well. But installing the certificates has not resolved the problem when I am logged into vSphere with a non-admin account, using either browser. I just get that same error every time.

However, when I log into vSphere with my administrative account, I can upload files to the "ISOs" folder just fine. Also, when I adjust the permissions of the "User Share" datastore and give the "vSphere Uploads" Active Directory group the Administrator role instead of the "Datastore Uploads" role, the users are able to upload files.

So is this a browser certificate issue, or a permissions/role privilege issue? If it's a permission or role privilege issue, obviously I don't want to leave the "vSphere Uploads" Active Directory group with an Administrator role on the datastore. But I can't figure out what other permission to assign to the role that will allow them to upload their files.

If this is a browser certificate issue, I'm not sure what else to try with the vSphere certificates not resolving the problem.