Sometimes you can get an idea by looking in the logs. Usually located at \Program Files (x86)\Ontap\smis\pegasus\logs
But a quick checklist of things I'd go for (off the top of my head):
1. Make sure the action account used to add the SMI-S provider into VMM is a local administrator on the SMI-S server.
2. Make sure the SMI-S provider and VMM are not on the same server.
3. Make sure the CIFS server is running on the SVM "cifs show -vserver <SVM name>"
4. Make sure the CIFS server is in the same domain as the VMM server.
5. Make sure the action account used to add the SMI-S provider is listed in the "cimuser -l" output on the SMI-S server (assuming authentication is enabled, which it is by default).