Cubemap Issue!

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I searched the forum for this error but didn't get any answers so here it goes. I get this line when i run compile:

Creating default cubemaps for env_cubemap using skybox materials:
skybox/grimmnight*.vmt
Run buildcubemaps in the engine to get the correct cube maps.

No such variable "$hdrbasetexture" for material "skybox/grimmnightrt"
Can't load skybox file skybox/grimmnight to build the default cubemap!

I know It't caused by the fact that I am using a non-hdr skybox texture.
How do i take care of this issue? I would prefer not to change skybox, only if it turns out that i can't solve this problem in any other way.

[BlisTer]

you can ignore this error

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I see, Thank you!