To reproduce this, just copy regedit.exe from Windows XP or Server 2003 and try to launch it in ReactOS.
It will fail due to the following missing dlls: clb.dll and ulib.dll (first it will notify about ulib, and after copying ulib.dll to system32, it will need clb).
The second one is totally undocumented by MS and completely missing on our side, but the first one we already have implemented: https://git.reactos.org/?p=reactos.git;a=tree;f=base/applications/regedit/clb;h=6a2d1c4539c37e4cffe6edeb9f9811625531d1a7;hb=HEAD. For now, it is just disabled, because it isn't used by anyone of our components. But it is used by MS Regedit as well, so it makes sense to enable this dll.
The purpose of this dll - Column List Box. As far as I teted, MS Regedit works just fine with our clb, I didn't notice any visible bugs.
After enabling it, MS Registry Editor needs only ulib.dll. Although this second dll is more difficult to implement it, due to absent documentation, now we lack only one dll instead of two. It's at least something.
I already made a fix in my local branch and will submit a fix soon.
Also it propably makes sense to move that dll into dll/win32, in order to not mix the dlls with exe applications.