I don't have any way of knowing what the rest of your code
is doing.
But within this section, you've got a
If (target.column mod "some number" = 0) then
...
...
...
end if
in this section, you're testing the target.value
and doing SOMETHING..
using Debug to step through the code  should tell
you what part of the code is actually putting a value in the cell.
but..
Right after the first IF... statement,
if you put:
If (target.value <> "") then
(remember to put the "End If" at the end)
I've sometimes had the above if statement return "null" instead of
"", so I usually use:
If (Target.Value & "X" <> "X") then
give that that a try.