Hi,
I used the mosaic from Raster Functions to mosaic my raster layers. But when I tried to export the mosaic raster using Data > Export Raster, it gave me an error message: Failed to export Mosaic Rasters: Failed to export the data.
It has worked fine for previous mosaic rasters. I've tried to mosaic the rasters again and export them, but it still didn't work.
I ran into this same issue today. Two rasters pasted fine, but the third failed, giving that generic error message. I tried Dan's suggestion, as well as a couple other methods, including exiting from Pro and trying to directly copy/paste the files in Explorer, which finally provided the more informative answer of not enough open space on my drive. Pro doesn't seem to know that. It just knows it didn't work.
Wow i got lucky, got stuck at same problem and thank god you provided the solution. (never really paid attention to red bar under c drive)
I fixed this by naming it with the '.tif' extension
I met the same problem. Its extension is tif and computer's space is enough.