First of all, the Flash-Over-Jtag.exe tools only supports DSP56800 core, for example, it only supports DSP56F801/803/805/807/826/827, it does not support DSP56800E core. The MC56F83xx including MC56F8357 use DSP56800E core, pls use the 56F800E Flash Programmer tools, you can download it from here:
Hope it can help you
BR
XiangJun Rong