I have no experience coding Lapper and I'm currently trying to get the source files running on my computer (with help of a professional programmer).
I did look into the Insim version issue and came to this conclusion:
In the file called 'Insim4.cs" a packet is created named "VER".
When looking at the Insim documentation "Insim.txt" that was the old way to do something with an Insim version number.
It appears that you now have to do that with a packed named "IS_ISI", which isn't used in the entire Lapper project.
Maybe this will put you on the right track to solve that issue.
I did look into the Insim version issue and came to this conclusion:
In the file called 'Insim4.cs" a packet is created named "VER".
When looking at the Insim documentation "Insim.txt" that was the old way to do something with an Insim version number.
It appears that you now have to do that with a packed named "IS_ISI", which isn't used in the entire Lapper project.
Maybe this will put you on the right track to solve that issue.