Welcome, from one guitar player to another.
I am a BAT user, not so much the VP MODPAK, but I believe if you are adding mods on top of a Steam-installed IL-2 1946, there are some things you have to do that are different from the traditional CD. Anything that is installed to one of the Windows protected directories, to include \Program Files and \Program Files 86 has to contend with potential errors because Windows is finicky... much better to install to a custom directory in the root.
In anyways. You will find that you will get more help if you use the Search box in the forum, because chances are your topic is already covered, and I do recall a discussion on these installations.
Good luck.
I play EXCLUSIVELY Ibanez guitars... and Fender... and Gibson... and BC Rich... and Jackson... and the kits I built... and Peavey... and uuhhh... anything really.