Hello Dylan,
I don’t remember exactly but at disk H:> properties> security I missed “Everyone”. I had added it and given permission for all actions.
Today I went through with it again and now have disk H: and disk M: compared in detail both sharing and security. I am now almost sure it is all right. I did notice that with disk H: settings were not made for Everyone, both in share and security. Forgot to allow something? To be on the safe side both disks closed and restarted to see if all settings are the same and unchanged. They are now. Also in security> advanced.
I will now check again if I can make a backup in disk H :.
…
Yes, it worked. What did I learn? So you not only have to check everything for share of both disk and folder, but you also have to check everything for protection> advanced and you need to see share and full management. You should also check whether your adjusted settings are actually implemented. I did that by closing both disks and turning them back on. If you forget something somewhere, it will not work.
Well this problem has been solved. Thanks to everyone who provided advice and assistance.
Greetings, Bert.