Do you have nonprinting characters and Hidden text displayed? If not, try
that first.
Then try selecting the rows above and below where you see the slightly
thicker gridline and press Ctrl+Spacebar. If a paragraph between the tables
has been formatted as 1 point, this will bring it back to normal size.
Also, make sure that the top row of the second table is not tagged as a
heading row (in fact, make sure that there are no heading rows except at the
top of the first table).
A common cause of being unable to make tables join ( though it's hard to see
how it could cause a split in the first place) is having one of them
wrapped. If you ever use the table handle to move a table (even if you just
inadvertently nudge it slightly), it will become wrapped, so go to the Table
tab of Table Properties for both tables and make sure text wrapping for both
is set to None. While you're there, make sure that the rest of the settings
on the Table tab are the same (table width, indent, etc.).
If none of the above is helpful, then it may be necessary to make sure that
all the column widths in the two tables are the same. This really shouldn't
make any difference, but some users have reported that having them slightly
different will cause Word to split the table. I would be more inclined to
suspect a conflict in other Table Properties such as those found in the
Table Options, but certainly it's worth trying every possible avenue.
--
Suzanne S. Barnhill
Microsoft MVP (Word)
Words into Type
Fairhope, Alabama USA
http://word.mvps.org