The following is the exerpt from VMware's vSphere 5 documentation - http://pubs.vmware.com/vsphere-50/index.jsp?topic=/com.vmware.wssdk.apiref.doc_50/vim.Datastore.html:
You may use the following characters in a path, but not in a datastore name: slash (/), backslash (\), and percent (%).
Please rename the datastore to be compliant with VMware standards.