TimeStampToDateTime - difference Delphi5 - Delphi7

[Cadere]

Hello,

On my computer I recently installed Delphi 7.
In my latest project I used to use this routine:

// in other routine: Starttime := GetTickCount();
// in other routne: perform action

function CalcTimeNeeded : string;
var Starttime,
delta : Comp;

begin
delta := GetTickCount() - StartTime;
result := FormatDateTime('hh"h":nn"m":ss"s":zzz"ms"',TimeSta mpToDateTime(MSecsToTimeStamp(delta)));
end;

In Delphi5 this works perfect. In Delphi7 I get an exception-error on TimeStampToDateTime.
How can I get this working in Delphi7 (or later???)

Thanks in Advance.
Jan.