Hi jensmander,
as far as I know I don't use encryption for my drives (think it is needed to set a pw and I can remeber that I havn't done that). I am not at home at the momnet and can't check it, sorry.
Yes, as the monment I am connected via 5GHz WIFI, but be also able to make connect a cable (just need to buy one which has the right lenght)
Alright (need to check the protocol option and what's set right now).
Maybe another information which is neccessary to find the root cause:
Some of the files I'd like to transfer to my Diskstation where the "ERROR 50..." message came up are originally coming from ab backup of the Photo Library from an old Diskstation (DS109+). Some years ago I moved them to an external 4TB HDD, since my 109+ was slow and wasn't fun to use anymore. I found a lot of @eaDir folders as well as Thumbs.db files on it, which I removed completely. But there is still the "ERROR 50..." message coming up each time I am trying to copy several folders with more than 800GB in total.