The relationship between the two objects cannot be defined because they are attached to different ObjectContext objects when updating a record

Question

I am getting the error "The relationship between the two objects cannot be defined because they are attached to different ObjectContext objects." when updating the permission record with UserRoles navigation.

var permission = _permissionService.GetPermissionRecordBySystemName(permissionSystemName);
if (permission != null) 
{
    var userRole = _userService.GetUserRoleById(roleId); 
    if (permission.UserRoles.Contains(userRole))
    {
        permission.UserRoles.Remove(userRole);
    }
    else
    {
        permission.UserRoles.Add(userRole);
    }
    _permissionService.Update(permission); // Error at this line
} 

I have used UnityContainer and repository pattern.

I have used EntityFramework(Code First). Following is the code of "PermissionRecord" class

public class PermissionRecord : BaseEntity
{
    private ICollection<UserRole> _userRoles;    

    public string Name { get; set; }    

    public string SystemName { get; set; }

    public string Category { get; set; }

    public virtual ICollection<UserRole> UserRoles
    {
        get => _userRoles ?? (_userRoles = new List<UserRole>());
        protected set => _userRoles = value;
    }    
}