Most of the time when you want to import your lab environment, most of the time we use folders to organize the datastores. But this is not the same when you want to import an OVF/OPVA template to one of your environments it brings an error. It is a bug in the vCenter Server 5.1.
Here is a small quote from the KB article KB2045635
This is a known issue affecting VMware vCenter Server 5.1.
Try one of the following workarounds:
Use vSphere Client to deploy.
Open the vSphere Client and use it to deploy the OVA/OVF file.
Use Web Client to deploy.
If the datastore is in a folder, remove it from the folder and try to deploy.
You solve this problem by moving the SDRS cluster and the datastores attached to the SDRS cluster from the yellow folder to the root folder inside the Storage view of the vSphere web client. You will be able to deploy the OVF/OVA template.