I’m not sure if it’s the best way, but what I have always done is to set a default texture to the Param2D. I usually use one of those that comes with the engine, inside the engine content. That will get rid of the error you see. Then, in a material instance, you can override those default textures with the ones you want.
THAT’S GREAT! Do you think you could maybe say how to do that? :~)
“set a default texture to the Param2D”
(I always figure everything out on my own): To do this there are a couple tricks: Assuming you have a material with Basecolor / AO, Normal, Roughness. Metallic etc. You may be tempted to click just one, like Basecolor, go into the Parameter Defaults tab (lower left near Details), and assign each matching texture to the corresponding Drop down (for Basecolor, Normal etc) If you do this they do not take! Only for the one you are on will the texture finally pop up in the node and that Nodes error go away…,. You need to do Basecolor, then select a different node, (say Normal), then back into the Parameter Defaults tab and tell it where only that texture is. Just do that for each texture and it should fix this Param2D error.
IF a texture node still says error, You may need to check and see (by clicking that texture node and looking at it’s detail panel (lower left) if that texture is perhaps a Color map? (but listed in the Details Tab Dropdown, as ‘Linear Grayscale’!!!) or vice versa …
It does still stay Param2D with this method, the only way to get a Texture 2D, would be to find the same texture the PARAM is complaining about in Content Browser (it should tell you where it is in a ‘Popup’) and drag in the texture as a Texture 2D. That will ALWAYS work :_)