[Solved] Merge to HDR not working

[PMeesters]

Hi community,

I want to merge 3 bracketed photo's. All Lightroom Classic can tell me is that he is unable to merge the photo's

The three photo's aren't that badly unaligned that it's impossible to merge. 
Photomatix has no problems creating a HDR from these pics.

What is wrong with LR Classic ?

How can I solve it ?

Why isn't there more info from LRClassic in the popup, with WHY it can't merge ??

All tips are welcome  🙂

Thanks

Paul

EDIT:

My apologies, one of the pictures was a JPG in stead of a DNG file.
Still, it would be nice if the process would tell us that not all the files have the same format.

[DdeGannes]

Are they all the same file type, i.e. raw, dng, tiff, jpg?

Do any files have layers?

Please provide some more info, the screen capture shows the forum guidelines.