SAMBA has a major problem when the WHEEL group contains root. Something (probably klUsrMgr) puts that in the %UNIXROOT%\etc\group file. Remove "root" from the wheel group (listed on the left side), and your problem will probably be solved (you may need to reboot).
FWIW, this nonsense should be resolved when SAMBA server 4 is finished, and installed.
My approach is to NEVER, ever, run klUsrMgr, until it has some actual use.