The BIT* functions work with 32 bit signed integers and you want unsigned 32 bit integer which VFP doesn't support. Depending on what you're trying to do, following may work for you

? VAL(TRANSFORM(bitlshift(0xff, 24), "@0"))

>I would like to shift a number between 0-255 to the left 24 times. When I do the following for example:
>
>

? bitlshift(0xff, 24)

>
>I should get: 4278190080
>
>However, I get the following number instead:
>-16777216
>
>How can I correct it?
>