Add Rasters to Mosaic Dataset Error

[AbdulRafay]

Hi,
I am using ArcGIS Desktop 10.7. I am having trouble adding Raster to Mosaic dataset. I am trying to put together data from landasat 7 etm, which I downloaded from EarthExplorer. Everytime I try to do that, it gives and error (screenshot attached). I have tried adding individual band layers (dataset), and folders (workspaces), but neither seems to work.
Can someone please tell me if I am doing anything wrong.
PS: I have turned off background processing as guided in one post. 

Kind regards

[JayantaPoddar]

You need to do a Mosaic for that.

1. Make a copy of 1 raster file. This will act as your target raster dataset where all other rasters will be added.

2. Use Mosaic (Data Management) to merge multiple existing raster datasets into the existing target raster dataset (Do not choose the Raster File that you have used as target, in input).

Alternatively, you may create a Mosaic Dataset, and add the desired Rasters to it.

[AbdulRafay]

Initially, I was trying to do that by adding rasters to Mosaic Dataset, but that was giving error.

I will now try it with the first method you have just mentioned.