Hello …
i have an assignment on Sunday … and i need to unfold my model 
…
unfortunately i’m totals beginner with sketchup …
and i created my models from cubes …
as you can see 
how can delete the dotted lines … (marked with red)
so i can unfold it with out measuring and cutting cubes manually ?
Thank you <3
Loos like you activated back lines (win shortcut: k)…
You haven’t supplied an example SKP.
But, I suspect these are ‘back-edges’…
Open your ‘Style’ settings and switch them off…
Report back if that doesn’t hide them…
If you want to actually remove those edges, you need to navigate in 3d and erase them…
When you say ‘unfold’… then how do you propose to do that ?
There are Plugins to do it, but you need to prepare your model…
e.g. SketchUp Plugins | PluginStore | SketchUcation
You might be better to group the ‘cubes’…
I’m still having the same problem …
Pepakura Designer still unfolding each cube by it self !! because the lines still there 
You want to make a solid out of it? You can try TIG SolidSolver or Thomthoms SolidInspector2 for this…
Check the orange line
the line still there inside the other cube
It says that it’s non solid or blocked
You could post the SKP, so we could look at it…
But you could initially try erasing some internal partitions/floors etc - which might help any Plugin trying to make it into a solid ?
My SolidSolver error-messages are much more extensive than you suggest… what did it say exactly ?
Can you post your model here? There is really not enough info in a picture to be certain what all problems you may have.
One thought: have you made every cube a separate Group or Component? If so, have you opened them one at a time for edit with View->Component Edit->Hide rest of model checked?
Yes every cube is created separately 
and then i moved it to the right place
So that answers my question! NONE of your cubes are separate Groups or Components. There are some of them that are “stuck” to each other. It is amazing that unfolding them worked at all!
Told you i’m totally new to the sketch up
how can i fix this problem without remake the model ?
Triple-click a face and watch entity info to see how many entities are selected. If it says 18 (6 faces + 12 edges = cube), right-click and select Make Group. Then hide that Group. Then try another face. Keep doing this until there are no more faces you can select without getting more than 18 entities. The remaining geometry has pieces that stick to each other, probably because they share either edges, corners, or faces. Edit them to clean up and make Groups.
Well it seems to be a long process with a 25 cube
This complex at the bottom center is all tangled up:
Yes sir 
Thank you verymuch … can you tell me what did you do ?
Here is a picture of the unfold … it needs some work but you can say that it’s done
(Looks like the same picture as before and not the result)
I’ve used the mentioned plugins to create one solid object without inner faces.
The beginner’s lesson here is a fundamental of how SketchUp works: geometry “sticks” to other geometry unless you isolate it by putting it in a Group or Component. The reason some of your cubes worked is that they passed through others without actually touching (i.e. without sharing an edge or face). The ones in the picture I posted all have shared face sections, which makes them stick together despite the internal edges that look like they are separate cubes.