"ISAM" is a term used in the database field and stands for "Indexed
Sequential Access Method", and refers to a particular way of getting at
data. It's actually quite an old term.
An "Installable ISAM" is to do with Microsoft's Jet database technology,
which is the technology on which Access was originally based. Jet is
designed to read/write .mdb format files, but it can also work with other
file types such as .dbf (Database), .txt, .xls and so on. There may be a
different Installable ISAM to enable Jet to work with each file type, or a
single Installable ISAM may work with several types (e.g. delimited text
files .txt, .asc, .csv etc.).
Since a standard Jet installation would typically have the Excel IISAM
installed, it is possible that either the IISAM installation or the Excel
document is damaged in some way.
Jet's successor "ACE" used in Office 2007 also uses IISAMs
When Word 2002 or later tries to merge from an Excel data source, it first
tries to use OLE DB (which would use Jet/ACE and the Excel IISAM), then ODBC
(which would also use Jet and the Excel IISAM) then DDE. It is just possible
that the first two are failing and Word is ending up using DDE, but I think
you might be seeing some more messages in that case.
