Problem:

When attempting to create a window that has 3 fields that occur 7 times per line for 20 lines

the following message is reported:

"You have attempted to add more than 255 gadgets to a window".

Can a window contain more than 255 gadgets?

Resolution:

The answer is that a window cannot contain more that 255 gadgets.

There is a limit in Dialog System that prohibits more than 255 objects (or gadgets) PER window.  This is documented under Dialog System Limits in the Dialog System Help or just type "limits" from the Help Index and double-click on the "Limits" topic. That would show the Dialog System Limits.