// Delete Duplicate Rows (re-entries)
NRows = N Rows(dt);
For(i = 1, i <= NRows, i++,
If(
dt:ID[i] == dt:ID[i + 1] & Data Table("Sheet1"):value1[i] == dt:value1[i + 1] & dt
:value2[i] == dt:value2[i + 1],
{dt << Delete Rows(i), i--}
)
);
I think this portion of your script in the braces is where things are going wrong (the if() function doesn't generally want braces there):
{ dt << Delete Rows (i), i --}
That being said, here's another, perhaps simpler way to get what you want, using JMP's built-in function for selecting duplicates:
dt << Select Duplicate Rows ({:ID, :Value 1, :Value 2});
dt << delete rows;