In general, we need more detail than this.

Do you have an Access table, and a SQL table that's supposed to
match it?  I would use Crystal Reports, with the main report accessing
the SQL table and a subreport accessing the Access table, then dump that
to Excel and re-sort it to find all the SQL records without a match on
the Access side.

Do you have a SQL table, and an Access database with a link to that
SQL table?  I would use Profiler to see what queries Access was sending
to SQL.  If the queries look correct, then maybe it's tripping over a
collation problem or something weird like that.