https://bugs.winehq.org/show_bug.cgi?id=42616
--- Comment #2 from Omega Software development@winomega.com --- Reproduced it again, this time with 1.8.0.
I think I found the factors that cause it. Steps to reproduce:
1. Remove ~/.wine and ~/.cache/wine.
2. Start wine directly to run the installer (womega.exe), before creating a prefix.
3. Since you removed Mono and Gecko installer from cache, a dialog asking to download Mono pops up, say yes (I think the same would happen with Gecko, but haven't tried).
4. When Mono download is aproximately at 60%, the installer starts, and at this point the wine prefix is not fully configured yet. The following errors are printed:
wineserver: could not save registry branch to system.reg : No such file or directory wineserver: could not save registry branch to userdef.reg : No such file or directory wineserver: could not save registry branch to user.reg : No such file or directory
and as a consequence %SystemDrive% cannot be resolved.
The problem might not be specific to InnoSetup after all. I expect any program attempting to resolve %SystemDrive would end the same.