>I did a SET DECIMALS TO 2, that was not the problem. The transform error seems to occur only in a compiled .exe, not from the command window. I did another test:
>
>transform(9999999.99,"999999999.99") returns "9999999.99" as expected.
>transform(10000000.01,"999999999.99") return "10000000.00" - not expected.
>
>Go figure (literally)!

I've just created a test project with only one test program included with the following lines:
?transform(9999999.99,"999999999.99") &&returns "9999999.99" as expected.
?transform(10000000.01,"999999999.99")

Both returned correct results...