OME 1.2 hangs at start screen

We just installed OME 1.2 on Windows Server 2008 R2. When I try to start it - it just hangs at the loading screen. The event logs are filled with this error (Event ID 0 in Source Essentials):

System.ArgumentNullException: Value cannot be null.
Parameter name: key
at System.Collections.Generic.Dictionary`2.Insert(TKey key, TValue value, Boolean add)
at Helpers.Extensions.WindowsGroupInfo.GetLocalGroups(IList`1 groupNames)
at DataProvider.Security.SecureUser.GetRoles(WindowsIdentity activeIdentity, SecureDataContext dataContext)
at DataProvider.Security.SecureUser.UpdateRoles()
at SmartConsole.Service.DataService.UpdateUserRoles()

Help?