Export Failed


I am trying Sql Export to dump database structure and data for backup purposes.
I installed last version available and launched it using an administrative account on a windows 2000 professional box.
I have no problems If I only export structure or structure + indexes, but the export fails when I try to export also the data.
The export terminates with the following error:
Export Failed
System.Byte Type Not Managed
(or something similar: I am translating it from italian)
Is there something I can do, apart from changing the dabase structure to avoid "not managed" data types?
Thank you very much.