Virtualbox :application error breakpoint has reached

[Lean_geek]

Then why that strange hd worked ?I found another such disk in that same machine which also worked.

Answering this question, marking it [solved] ,close the issue.
This is my last post on this topic also.

[socratis]

Then why that strange hd worked ?

Well, you may not be the only one. Here is a really, really closely related ticket about a Win98 ISO which was failing: #17690: Windows 98SE will not install (crash, no VT-x available).

Turns out it's a hidden, specially triggered bug in VirtualBox. From the comments of one of the developers (emphasis mine):

Actually no, Windows 98 does not need VT-x, but there is some bug in the non-VT-x execution engine. For whatever reason the bug only affects 32-bit hosts, not 64-bit hosts. So if you enabled VT-x and the problem is gone for you that's great, but for us the bug remains and we still need to fix it.
...
This particular crash is far from new, it goes at least as far back as 4.3.40. I'm beginning to wonder if it ever worked. It's something about that particular Windows 98 SE bootable ISO.
...
The crash does not happen with VirtualBox 4.2.36 (or 4.2.30 or 4.1.36 or 4.0.14). It does happen with 4.3.0 and likely all following versions. So this broke between the 4.2 and 4.3 series, several years ago.

I would suggest to add a "me too" with your details in the ticket. Besides the ISO that the developers have, you have a bootable floppy with the same issue it seems.

So, this topic is not [Solved]. Yet...

[Lean_geek]

I think it's a binary tramslation type error, in which incorrect instruction occures... It is certainly a bug.

I'm eating my words, but I have said it long ago. The chance of getting out of the bug is small, as mpack said. Indeed sw virtualization is almost dead.