Tried to switch to a background that was never loaded

Hey
I upgraded to Stepmania 5.4 some days ago, and since then I'm getting some error message during some songs saying
"Tried to switch to a background that was never loaded:
<BackgroundDef File1='white flash'/>"

Can anybody help me with that, the message is pretty distracting when playing.

Create a folder named "white flash" inside stepmania's BGAnimations folder.
Create the a file named "default.lua" inside that folder.
Put this in that file:

return Def.Quad {    

    InitCommand=cmd(x,SCREEN_CENTER_X;y,SCREEN_CENTER_Y;scaletoclipped,SCREEN_WIDTH*2,SCREEN_HEIGHT*2);

    GainFocusCommand=cmd(finishtweening;diffusealpha,1;accelerate,0.6;diffusealpha,0);

};

If you previously deleted the BGAnimations because they're irritating, then just put this instead:

return Def.Actor{} 

Other common BGAnimations (i.e., ones that are packaged with stepmania):
flash:

local flashColor = color(Var "Color1")

return Def.Quad {

	InitCommand=cmd(x,SCREEN_CENTER_X;y,SCREEN_CENTER_Y;scaletoclipped,SCREEN_WIDTH*2,SCREEN_HEIGHT*2;diffuse,flashColor;);

	GainFocusCommand=cmd(finishtweening;diffusealpha,1;accelerate,0.6;diffusealpha,0);

};

white reverse flash:

return Def.Quad {    

    InitCommand=cmd(x,SCREEN_CENTER_X;y,SCREEN_CENTER_Y;scaletoclipped,SCREEN_WIDTH*2,SCREEN_HEIGHT*2);

    GainFocusCommand=cmd(finishtweening;diffusealpha,0;accelerate,0.6;diffusealpha,1);

};

yellow flash:

return Def.Quad {

    InitCommand=cmd(x,SCREEN_CENTER_X;y,SCREEN_CENTER_Y;scaletoclipped,SCREEN_WIDTH*2,SCREEN_HEIGHT*2);

    GainFocusCommand=cmd(finishtweening;diffuse,color("#FFFFA0");accelerate,0.6;diffusealpha,0);

};

Thanks for the response, it worked. Though I decided to remove them again, since it is indeed somewhat irritating, so another thanks for saying how to do that in advance. I don't know why they were missing in the first place, since I cannot remember deleting something Stepmania-related that's not Songs but well, whatever. :D

I don't like the backgrounds that are just a brief flash, I find them an irritating distraction too. It took me a bit of searching to even find a simfile that used them to test my fix.

Had I known they were that "rare" I could've named you about 5 or 6 already. Just my luck I guess.
I don't mind rapidly changing background pictures or videos at all, but those flashes (and to some lesser degree the error messages) were really disruptive. I'm glad to be rid of both now.

I still confused can you help me please

What part has you confused?
If you paste the exact text of what you're seeing I can probably tell you how to fix it.