Cut out a Scene with subset

I want to cut out a spezific Part of a Landsat 7 scene.
For that i used the export function and the subset to cut out a Part of the Scene.
When i export it´s not the Scene i want to Export and the Scene gets cut in serveral Parts.
I have additionally another problem. I want to put a Band in another Data set and wanted to make it with the Band math tool. There i usually just put the Target Product i want and can than use it in another Data set. That dont work anymore and i dont know why.
Thank you for your help!
best regards
Martin Feldmann

Hi Martin,

So, I understand you first subset the scenes and then save it as .dim or export as other format, right?
About copying bands with band math, you images should be in the same orbit and have the same size, if not it will not work.

yes i use first the subset and than i save it.
I used Landsat 7 images for copy it and i already did this before.