I had the same problem with my ls-chl (1TB) with firmware 1.07. I had a folder to which I could only connect to as admin. The user I added was identical to my windows user. As soon as I tried to login with this user it did'nt work (Username or password wrong). Not even after deleting all network connections to the ls-chl and attempting to connect via "net use ... /USER:myUser".
The problem was gone as soon as I deletet all users, all usergroups and redefined only the users (without any groups) I gave permission to the share only on userlevel. Two users were able to login at the same time.
Anyhow when I logged in to the nas via web with the admin account both users lost their connection to the share and could not reconnect. Only after I deletet the users and redefined them.
It ist not satisfying and does not seem to be very stable.