www.makemkv.com

I've ripped a BD not as MKV but folder. Now I wanted to open this folder on HDD using File > Open File, after opening the index file nothing happens, even though I've not ripped in a long time I'm rather sure this has worked before. As workaround I rip it now a second time to MKV from optical disc. I'll report back if it happens again on my next BD.

edit: sorry but I missed that it probably was ripped by another software, I thought it was ripped by MakeMKV

If you've ripped it to a folder, depending on what you wanted to do, there might be other software that would work.

For example, if you wanted to convert the contents to MKV or MP4 files, handbrake (from handbrake.fr) will do that from a BD folder structure, while also making the resulting files smaller through better compression.

or staxrip