Raster projection defined, but unknown geographic coordinate system?

[KathleenHoenke]

When trying to mosaic two rasters, I noticed one had a projection but an unknown datum and therefore couldn't be mosaicked to the other. I attempted to define projection to what it should be and it definitely was not correct. Now, no matter what I do, I can't seem to define the correct projection and have it show up in the right place, and is now not even show ing up at all. Is there a way to fix this issue without having to recreate all of the rasters from scratch?

[DanPatterson · Accepted solution]

You have to define it back to what it was.

If the file was a *.tif, you could try deleting/renaming any file with the same name but different extension to (eg a *.tfw, *aux etc)