Do you restart Hyper-V hosts after giving permitions to the network share? Host get this permitions only after restart.
You post "Failed to create export directory with error 'General access denied error'(0x80070005)", so...
What kind of permitions do you give to hyper-v host? Maybe it havn't rights to create/remove folders?
Also, check the path, what you want to create by your script.
Waiting for reply. :)