Yes, I see that now but if I try
currentSpaceId = SymbolUtilityServices.GetBlockModelSpaceId(HostApplicationServices.WorkingDatabase);
using references to autocad 2006 the compiler gives me this error:
An object reference is required for the nonstatic field, method, or property 'Autodesk.AutoCAD.DatabaseServices.SymbolUtilityServices.GetBlockModelSpaceId(Autodesk.AutoCAD.DatabaseServices.Database)' (CS0120)