Did you choose to convert a folder or a file? You probably need to choose to convert a folder if you're converting a folder.

I don't see a "convert folder" option on the menu, just buttons that make me open a file.

Hmm...
What happens when you open the .exe?
I get a small window asking me what I want to convert to from (Build-wise) and afterwards the option to convert a folder or a fiile.
Then again I might be talking about a completely different mod converter, but try redownloading.

Are you sure? I just re-downloaded the release on this website and the window progression goes

1. Chose Conversion Type (Build 13 to 22, Build 19 to 22 or Build 21 to 22)
2. Choose Folder/File
3. Select Folder/File
4. Upconvert/Downconvert Dialog.

I should probably updated this for B23, could anyone tell me the specific conversions that are required?

Paths for skeletons and zombies have been moved to the Undead.rte.
Paths for crabs have been moved to Wildlife.rte.
Various paths within .rtes, predominantly Coalition and Dummy.
No PresetName that will be shown on the buy menu apart from the build stage may have a single word 11 characters long (a single word means any continuous string without any spaces).
Pretty much nothing else has changed though.

well, I pressed the "other" option when I opened the converter, 'cause I don't know what version Darklone mod is. Anyone tell me what version it is?

Try for b21 to b22. It won't break anything if you get it wrong.

it did
I had to reinstall cortex command.

anyone know what version DarkLone is?

Only select Darklone.rte for conversion.

Ok, the conversion was successful, but when I plug it into Cortex Command, I can't open any missions, the screen just turns black and does nothing.

Search for the word Flamethrower. Separate it into flame thrower.

In the mod or the converter?

Well the mod, supposedly. That's what the game's loading isn't it?

oh yeah, that was obvious, but I do not really see how it would help. Care to explain?

The reason it is hanging with a black screen is related to a feature implemented new in b23. Word wrapping. Before, in b22 and earlier, when you made an overly long PresetName for a buyable item, it simple trailed off the buy menu button and disappeared at the end of the buy menu. In b23, Cortex attempts to wrap text so that it stays within the button, but it can't handle overly long strings of characters that are not separated by spaces. So, when given a word that is longer than the width of the button, it hangs to a black screen. That maximum width has been experimentally determined to be around 11 characters, so any PresetName of a buyable object must have a space within 11 characters of unbroken text. Hyphens and underscores do not work.

tl;dr b23 requires PresetNames to have spaces within 11 nonspace characters.