I know how to compile it however I'm moreso curious about how you are getting it from the folder its in to a place where it can be compiled... or do you have the ini pointing just to the files folder (ie \mystic\files\nodelists) etc.
Does mystic know which archive to use?  I can see it working fine like that until a new year then it could be an issue?
What I've done to make things easier is to breakout different sections of the original "mutil.ini" file into sectons.  One I call nodelist.ini.  In it, you need to have the location of your different nodelist files defined.  Another one I broke out, I call mailin.ini. The original mutil.ini has examples that you can follow.  You just need to define, for instance, node numbers with local file locations.  
As to archiver, the node lists I'm getting are all using the "zip" archiver.
If I remember correctly, you set that option up when applying for a node number.
Here's a github site (
https://github.com/christiansacks/tqw_mutil_inis) where Christian Sacks (tqwnet, the quantum wormhole), uploaded a bunch of his *.ini files.  That may help you more than slogging through the whole mutil.ini file.
If those files don't help, post again and we'll keep at it!
ogg
Sysop, Altair IV BBS
altairiv.ddns.net:2323
... Fer sell cheep: BBS spel chekker. Wurks grate.
--- Mystic BBS v1.12 A49 2023/04/30 (Windows/32)
 * Origin: Altair IV BBS (1:106/1)