You are likely to see this problem if you are inserting your data using
fields which are not completely blank (e.g. have a single space in them), or
if you are using an ADDRESSBLOCK field and, for example, you have a last
name but no title or first name (see my nearby message in response to Dee's
message, which describes a similar problemexcept that in your case you
probably need to look at what is in the first line of the ADDRESSBLOCK).
It's difficult to prescribe a solution without knowing the exact cause - if
there are spaces in your data, try to remove them. If it's an ADDRESSBLOCK
problem, you probably need to use individual fields instead, nested inside
IF fields. That's a bit more complicated so let's be sure that the problem
is ADDRESSBLOCK first - if not, let us know.