When you first start up the flowchart, the dialog limits your number of
rows/columns. But you can get more afterwards. Do this, for example:
1. Start with 1 lane
2. Shrink the width or height of your colum manually.
3. Now just copy it with Ctrl + Drag
The add-on (startup dialog) is probably calculating how many default lanes
will fit on the page and is being "nice" to you, in not letting you choose
too many that they run off the page.
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Hope this helps,
Chris Roth
Visio MVP