For the suppress blank line feature to work
a. the line must have at least one MERGEFIELD field on it, and nothing else
that will result in any text, not even any spaces
b. the result of the MERGEFIELD must be completely blank, i.e. not even
contain any spaces

Do not expect the feature to remove other empty lines - for example, if your
address is a multiline address that is inserted using a dsingle merge field,
blank lines within the address will probably not be suppressed.

If you are using Word 2002 or 2003 (it doesn't sound like it) then this
feature does not work when the fields are nested within fields such as IF
fields.