Yes, you are correct. My calculation wasn't accurate.
But according to my tests, it causes problems for Columns.Count > 100, exactly like you say. I was trying a simple loop in Page_Load:
for (int i = 0; i < 100; i++)
{
DayPilotCalendar1.Columns.Add(i.ToString(), i.ToString());
}
But isn't it possible that you already have some Columns defined in the .aspx template (I would guess for 2 columns) and add more columns in the code behind without calling DayPilotCalendar1.Columns.Clear() first?
I also realized that although IE can work with div.style.width in decimal percent (10.2%) it generates an error for td.style.width with the same value. I will try using minimum of 1% width for all columns (IE should shrink the width automatically).