Right-click on both of those datastores and verify whether there's a folder in each one called VMNAME.
If there's a folder in only 1, then you probably have an ISO mounted on the VM and it's located on the second datastore.
If there's a folder for the VM in both datastores, check inside and see if both folders have a .vmdk inside. If they both have the disk VMDK file, then you probably got in a situation where a storage vMotion didn't completely finish up and the old files were left hanging around on the old datastore. This happens a fair bit. To fix, right-click the VM and select 'Edit Settings'. Select the hard disk device, and make a note of the datastore it's on. You can then safely delete the VMDK in the other datastore.
It's also possible to have a VM's configuration files on one datastore, and the VMDK hard drive file on another datastore. So if you find a folder for the VM in both locations, see if one of them has the .vmx, and the other one has the .vmdk. You can easily get around this problem by storage vMotioning the VM to an entirely different datastore.