Ok, This was driving me nuts because my problem matched those discussed here, but the solution didn't work for me. I did finally figure out how to fix it though.
First off, it seams like the description about it being referenced someplace is correct. I.e. that esxi is preventing a rename or creation because i thinks there might be a datastore by the name used already there. In my case this was with NFS, where I was naming the datastore identically on each host. One host still had it and it was working, the 2nd host did not list it, and if I tried to add it with the same name it would append a (1) and not allow a rename (or depending on the method used to create it, it would actually refuse to create it).
My solution? well, I didn't find out what was referencing it, but since vCenter was trying to keep things correct/safe/etc, I used that and theorized that if I renamed the existing working datastore on all hosts that it would change the item I couldn't find to also point to said new name. As a bonus, since vCenter does everything live, this didn't affect anything in production or require any kind of reboot.
To be clear/simple, here is what I did to fix it:
1. Delete any datastore name that I was trying to create (for instance any that are not yet used and were/are getting a (1) appended to the end).
2. Connect to the vCenter Server with the vSphere client, and select Home>Inventory>Datastores and Datastore Clusters
3. Find the WORKING datastore with the same name giving you difficulty and rename it (i.e. append the word TEMP to the end, which is what I did)
4. Immediately (or if your cautious, like me, wait a few mins to ensure changes have made it/replicated/etc) rename it back to the original name
5. Go to the host giving you difficulty and try adding the datastore back, if your error was similar to mine it should allow you to add it without error or appending a (1)
Depending on the situation you might reverse steps 4 and 5's order, however I haven't run into this more than once to envision when/why.
That all being said, I did this on a non-critical server that I could have just turned off without issue, you may take my word that it didn't affect production but that won't do you much good if it blows up in your face, so take the right risks for your environment. (Obligatory YMMV)
cheers