In order not to waste Dmitries precious developer time, I will try to fill in the gaps
Dmitry, your explanation fills in some holes but does not explain why if our computers have been running for more that a week we can start, for example, Open office 4.12 but if after closing it we can not start vBox 5.06 and trying to restart OO throws a fault of not being able to open SC.DLL. At that stage even EPM which we use as our standard text editor stops responding and we have to reboot.
The reason is quite simple, though not really obvious: Todays applications (such as OpenOffice or Vbox) are so demanding with respect of memory, address space that we are continuosly bouncing into the limits of our beloved OS/2. Just remember: Back then NO application required that much memory, address space and the like. While we are (theoretically) within the bounderies of OS/2, nobody at IBM back then tested, whether an application that huge still worked under alle circumstances - simply because there was NOT A SINGLE application that huge. The possibilities why something might fail are endless and one especially annoying issue is that the OS fails to free ALL resources these huge applications need when running. So: After a week (or earlier) some resource of the OS has been so badly eaten up, or fragmented, or.... that you have to reboot.
Software from back then never used up enough resources to even show the problem, because it simply would take too long.
It has worked for years without problems but now ....
Sure. Use the software you used back then it will still work endlessly. That is not an option? We know that is why we are here....
However, we do not have the source code to OS/2. Unfortunately.