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And again... replace all memory re/de/allocation with macros, that'll make it easier to debug memory related issues :)

Thanks to everybody helping and my stupidity I got program working.  Big problem was here, I don't know how I missed it before but sometimes even the most obvious mistakes are invisible to the people making them:

     invoke GlobalSize,hMemory
     mov ecx,eax
     mov edi,pMemory 
     xor eax,eax
     mov ax,7a63h

    @Begin:

		.if ecx<=00h
		    jmp @End

		.else
		    stosw
    sub ecx,02h
		    jmp @Begin

        .endif

    @End:

This works perfectly for files whose lengths are even numbers.  If file is odd number length then ecx ends up as 1 which is greater than 0 so two bytes are written and ecx ends up with a value of -1.  Of course it is too late and one byte has been written into illegal address space.  So I changed code to this and works good.  No more exceptions:

	 invoke GlobalSize,hMemory
     mov ecx,eax
     mov edi,pMemory 
	     xor eax,eax
     mov ax,7a63h

    @Begin:

		.if ecx==00h
		    jmp @End

		.elseif ecx==1
		    xor eax,eax
		    mov al,63h
		    stosb
		    sub ecx,01h
		    jmp @Begin

		.else
		    stosw
    sub ecx,02h
		    jmp @Begin

        .endif

    @End:

best regards,

czDrillard

I just hope you know what you are doing in the future. The code don't look very friendly. For your case ecx == 1 why do you have to dec ecx and then jmp back to @begin when you can jmp straight to @end

Personally I don't recommend mixing jmps with .if/.while etc etc