Problem med at skrive data og så læse det igen

Davs...

Jeg sidder og roder med komprimering og har oprette to funktioner til at klare det. Mit problem er at jeg ikke kan få det dekomprimeret igen, ZDeCompress giver fejlen "data error". Så fejlen ligger nok i at jeg gemmer forkert, men jeg kan ikke hvad jeg gør galt.

På forhånd tak.
  rrm

function TCompress.CompressAndWrite(tFile: TFileStream; buffer: Pointer; size: integer): boolean;
  var
      compressBuffer: Pointer;
      bufferSize: Integer;
      writeBuffer: string;
  begin

      Result := false;

      // TFileStream not valid.
      if(tFile = nil) then exit;

      try

        // Compress the buffer.
        ZCompress(buffer, size, compressBuffer, bufferSize, compressLevel);

        // Allocate memory.
        //GetMem(writeBuffer, buffersize);
        SetLength(writeBuffer, bufferSize);

        move(compressbuffer^, Pointer(writeBuffer)^, bufferSize);

        // Write the buffer size.
              tFile.WriteBuffer(bufferSize, sizeOf(bufferSize));
            // Write the buffer...
            tFile.WriteBuffer(writeBuffer, bufferSize);

        // Free the buffer
      //  FreeMem(writeBuffer);
        FreeMem(compressBuffer);

      except
        on EOutOfMemory do exit;
        on EWriteError do exit;
        on Exception do exit;
      end;

      Result := true;

  end;

  function TCompress.ReadAndDecompress(tFile: TFileStream; out buffer: Pointer; out size: integer): boolean;
  var
      decompressBuffer, readBuffer: Pointer;
      bufferSize, decompressSize: Integer;

  begin

      Result := false;

      // TFileStream not valid.
      if(tFile = nil) then exit;

      try

        // Read the buffer size.
              tFile.ReadBuffer(bufferSize, sizeOf(bufferSize));
            // Write the buffer...
            tFile.ReadBuffer(readBuffer, bufferSize);

        // Compress the buffer.
        ZDeCompress(readBuffer, buffersize, decompressBuffer, decompressSize);

        // Allocate memory.
        GetMem(buffer, decompressSize);

        move(decompressBuffer^, buffer^, decompressSize);

        size := decompressSize;

        // Free the buffer
        FreeMem(readBuffer);
        FreeMem(decompressBuffer);

      except
        on EOutOfMemory do exit;
        on EWriteError do exit;
        on Exception do exit;
      end;

      Result := true;

  end;