I ran into this same issue when moving files from my laptop to my desktop. Here's the fixDJ DiY wrote: I would like to know witch, because if an other win10 user runs into this problem, your experience could help.
C:\Program Files (or wherever you installed LMMS) > Program Files > LMMS should be there, so right click and go to Properties > Security then edit the privileges to give full control to the local user. Hope this helps anyone else with the writing error.