With the mod "Factory Planner" (https://mods.factorio.com/mod/factoryplanner) it says when I want to introduce the production of some molten ore that there is not recipe (https://i.imgur.com/M5x207e.png) on the top left corner but I can set the recipe on a smelter.

Molten ores aren't made in furnaces but in assembling machines which just look like furnaces. Thats because furnaces can't handle fluids and are restricted to 1 ingredient. Also there can't be more than 1 recipe for each product like with molten-ore to plates and ore to plates.
Therefor both, smelters and casters are assembling-machines.

Also i've found the error causing the missing icons.

I mean that the mod Factory Planner doesnt detect any recipe for making any mokten ore, so I cant introduce it to the calculation of whatever factory I want to make. But its weird because I can select the recipe on the smelters.

https://i.imgur.com/GXpmX1h.png

https://i.imgur.com/pGur6Z3.jpg
Maybe save the game with factory planner disabled and then reload it with the planner enabled?

Yes, I can introduce the recipe for plates on the Factory Planner but I cant for any of the molten ores.

Try to left-click the molten iron icon and it should add a new line to produce 9.6k molten iron/second, thats the thing that gives me an error.

Ah, i see. Hm thats weird. I can att the recipe by hand like so:
https://imgur.com/LGSrWIn
but right-click also gives me an error. Since all recipes are there and working i suspect that factory planner does something weird.

EDIT:
https://mods.factorio.com/mod/factoryplanner/discussion/61f3256f72279324ab8e5ab3

Well, it sems that it has something todo with temperatures.
I will add an option to disable temperatures on fluids and hope that therenas will fix it at some point.

EDIT2:
https://imgur.com/accRhxJ
https://imgur.com/jGABJPm
Removing Temperatures and using the matrix solver seems to fix the issue and also it doesn't have any sideeffects so far.

EDIT3:
https://imgur.com/MuU86OL
So, no fix. :(