[fpc-pascal] DLL call works on FPC 2.6.4 but not with D7

[Paul Breneman]

Below is code from a C program (that works).

 From the ".h" files:
typedef uint32_t PICO_INFO;
typedef uint32_t PICO_STATUS;

PREF0 PREF1 PICO_STATUS PREF2 PREF3 (ps5000aGetUnitInfo)
(
   int16_t      handle,
   int8_t		*  string,
   int16_t      stringLength,
   int16_t     *requiredSize,
   PICO_INFO  info
);

 From a ".c" program:
	int16_t i = 0;
	int16_t requiredSize = 0;
	int8_t line [10];
	PICO_STATUS status = PICO_OK;
status = ps5000aGetUnitInfo(unit->handle, line, sizeof (line), 
&requiredSize, i);

**************

Here is the dll call I'm having trouble with:
function ps5000aGetUnitInfo
          (handle : smallInt;
           var str : Pchar;
           stringLength : smallInt;
           var requiredSize : smallInt;
           info : integer
           ) : integer;
{$IFDEF WIN32} stdcall; external 'ps5000a.dll';{$ENDIF}

I have two console programs that are almost identical.

Here is my FPC 2.6.4 call (that works):
       Status := ps5000aGetUnitInfo( ps5000a_handle, MyReturnStr, 
StringLen, requiredSize, RInfo);

Here is my D7 call (that doesn't work):
       Status := ps5000aGetUnitInfo( ps5000a_handle, @MyReturnStr, 
StringLen, requiredSize, RInfo);

In D7 I have to add "@" on "MyReturnStr or the program crashes.  With 
the "@" added the program doesn't crash, but things still don't work.

Any suggestions on what to look at?