SMB lock preferences appeared overnight.

Hello, I am running Kodi on my ATV4 and have my movies etc on a Win10 PC.
Last night I watched a movie from my PC through the atv4 with no problems at all and have been doing this for awhile now without issues. I shut down the Atv4 but left my PC running.
This morning I tried watching another movie and Kodi brought up the smb lock preferences dialogue where I had to enter a username and password. I can’t work out why just overnight this would have happened as I didnt make any changes to the Win10 machine at all.

I tried the following.
1. Removed the stupid windows live password and username that I had setup to log into my machine (even though it worked fine with this before anyway)
2. Changed file encryption in network sharing settings to 40 bit
3. I tried to add a new user but in Windows 10 you have to add an email address and all this other crap. I then found a way to add a new user in computer management> local users and groups, so added the user Kodi and then added my ha5d drive again and this worked.

But why did I even need to do this in the first place. It worked fine for mo this and months without all this then over night it changes and I can’t work out why?