let's see if we can debug your issue.
If you use Chrome or Firefox try to connect with vOneCloud User Interface, and open the Development Tools (Ctrl + Shift + I).
Then with the development tools opened try to get the Datastores, not importing them just get the list of available datastores.
Look in the Network tab of the Development Tools
Browse the requests found in the Network tab and look for a query that starts or contains datastores?:
Click on the URL you should see a JSON response generated by vOneCloud.
Could you please post the text contained between curly braces (JSON)?
That will help to debug what prevents the datastore to be imported. Before posting check if the text contains sensitive information that you don't want to share.
Also a final question what's the name of the datastore you're trying to import?