MBUtility requires data to be in a very particular XML format, and it's not always easy to determine the format you need. Always try out operations on a test database before you try to import anything into your real database. Also make sure to back up your database before you begin using MBUtility, so that you can recover if anything goes wrong.
You can make life easier for yourself if you use MainBoss itself to see what data formats are required. For example, suppose you want to import unit data. In a test MainBoss database, create a few unit records, then export them with MBUtility (see Exporting Data from Your Database and An Example of Exporting to Excel). Export the unit records to Microsoft Excel so you can see what unit records should look like. Then manipulate the data you want to import so that it looks the same. (You can do this in Excel.) When the data is ready to be imported, you can use the MBUtility import operation to put it into a MainBoss database.
Importing a record is conceptually identical to clicking a New button in MainBoss. For example, importing information about an item has the same effect as using New Item to create a new item record.
Most MainBoss records have a unique identifier of some kind. For example, the Code field of an item record must be unique; you can't have two items with the same code. MainBoss will give you an error message if you try to create a new item record with the same Code as an existing item.
The same applies when importing data. Importing an item record has the same effect as New Item, and MainBoss will give you an error if the imported record has the same Code as an item that's already in the database. If this happens, it usually means that you tried to import the same item twice.