Log in as the service account on the DX server and try to write a file to the specified path.

Try enabling additional logging using the DX Admin. Go to Service>Event Settings>Trace
Check the box next to Extended drive meta-data export, then click OK
Right click on the extended drive and click Force Meta-Data Export
Post the results. Perhaps we can shed a little light here.

I tried logging in with the service admin and I could create a file in the specified folder, but when I tried the export it failed again with the same error(3).

MSG 04/06 10:12:29 (3716) Filter D: status changed to 6.
MSG 04/06 10:12:29 (3348) Meta-data export for extended drive D: has started.
MSG 04/06 10:12:29 (3348) Extended drive backup of "D:" started.
MSG 04/06 10:19:48 (3348) Extended drive backup of "D:" stopped.
MSG 04/06 10:19:48 (3348) Filter D: status changed to 1.
ERR 04/06 10:19:48 (3348) [Dm_FilterBackup.cpp, 371] Meta-data export for extended drive D:
encountered an unrecoverable error (3).
Here is the event logs from DX .

Sorry, I thought we'd get more info.
Have you successfully exported using another path?

I have not had any successful metadata exports of the server.

So that rules out the path. Sorry Watts, I give up.
You may have to contact support. If you would please post back the resolution.
Thanks