The Wizard uses your input to make a new hidden worksheet within the book
that exports data to the database. (If you are familiar with VB, you can see
that the sheet is listed there as "very hidden." Unhide it, and you can see
exactly what the Wizard has set up.) This new sheet esentially stores all of
the values and references that you indicated you wanted exported when you
went through the Wizard menus. If the formatting of the headers in your
database aren't exactly the same as the ones in the hidden worksheet (and I
mean exact, down to capitalization), if the number of cells it thinks it
needs to export doesn't match the number that are listed across the hidden
sheet, if there is an extra column in the database, the Wizard gives you the
structure error. In my experience, it has saved the data anyway except for
the columns that don't match perfectly.
If you are brave enough to go in and mess with it, I would suggest opening
the file with Visual Basic and unhiding the TemplateInformation sheet. You
can then go through and check each column in the hidden worksheet to each in
the database for spelling, extra columns, etc. and make sure that the
"Number of columns" cell on the hidden sheet matches the number of columns
listed below.
Note that if you have added/subtracted values to be exported and modified
the database, older files based on a previous version of the template will
give you the structure error because they no longer match the altered
database.
Good luck!