are you sure you have the full share and folder path specified? from your screen shot it looks like something may be missing... normally it should be somthing like smb://server/share/folder/
(in my screen below the share is /exports and the folder I'm importing from is /EmptyImportShell which I created doing a VM export to the /exports share previously ... in that /EmptyImportshell folder is a file called EmptyImportShell.xml which has all the metadata about the VM and one qcow2 file which in this case happens to be 93dfb769-5ccd-49af-90c6-dd464b03536d.qcow2 ... but it's a guid so your file name will be different)
But as a test, if you haven't already can you create a small "template" VM with 1 small virtual disk (don't even have to boot it) and try to export it to that same server / share / credentials to validate that the export works ... and that you can import it back in as a test.
If you can export that empty shell and then test import it back ... that should at least confirm all the permissions, paths, etc. are correct... then you can even use that empty template to replace the virtual disk file with the virtual disk you want to import ... just replace it but keep the name and extension the same and give it a go.