So I had the same issue as you.. I played around a bit and found a solution to this.
Atleast it worked for me.
What I did is that I opened the ops.json file with the Notepad, deleted whatever was previously written and typed in the Names of the players I wanted to give OP to, just like you'd normally do.
Then I hit ''Save as'' and that's where things change a little, instead of saving right away make sure you add ''.txt'' (ops.txt) at the end of the file's name... Launch the server, join in and try to change the game mode to see if it works.
Since Minecraft Version 1.7.8 was released, I downloaded a new Server. now I'm not able to get op rights anymore. Have you got any ideas how to do it in Version 1.7.8?
I had the same problem Upgrading from server 1.7.5 to 1.7.6 carried all the OP and whitelist permissions over and allowed 1.7.8 clients to log on. Upgrading from server 1.7.6 to 1.7.8 wiped out all the OP permission and Whitelist permissions on the server. I assume it also wiped out ban lists but I didn't have any. If you have large groups whitelisted or banned you may want to keep track of all the names before upgrading.
I guess the server console is the best route to recreate these permissions after upgrading to 1.7.8. . Whatever you do don't downgrade to 1.7.5 again to get your lists back unless you are also restoring a save. All the character data will be gone on the map.
When you host your server the console should be the first thing to come up... Its the box with the java icon on the bottom right is where your should type the command *op burner624* or whatever your username may be
The ops and whitelist files have become pretty useless since you can't edit them in notepad++ anymore, you need this UUID thing.
This is one of these useless changes in minecraft, just as the removal of the item ID numbers, I know most of 'em by hard and they were easy to use in commands, e.g. [/give shadz159 152] instead of [/give shadz159 minecraft:redstone_block]
Another weird thing is the empty server console, It's just became a white, empty and useless screen.
Can somebody explain to me why this UUID thing is used? Everything worked fine before it was there as well.
Yes, the name system worked before, but with name changes imminent and teasers already going out, Minecraft needed a way to still track players without names as the names could change at any time but you don't want your stuff gone. UUIDs were the solution. And players have always had them, it's only just now they've been really used.
As for the item thing, same deal. It worked before fine, but it was also annoying as hell to memorize (how did you do it?) and this way it's easy to do, but also with Mojang being expected to live up to its long-ignored promise of a modding API, they needed a way to resolve ID conflicts quickly and efficiently. Also, you don't actually have to type minecraft: although you do have to type the modname if it's from a mod.
I wrote my name in ops.txt and became ops.json and my name was still here, but I don't have op rights. I have only an useless compass in slot 5 of my inventory (if i right click nothing happens because the server is new and I didn't register it) and can't destroy anything (bukkit plugins)...