Thanks, Chris.
I've checked the Hauptwerk v4 component installer source code briefly, and the error handling appears fine. I also briefly tested v4 by trying to install a few RAR5-format Hauptwerk component installer files, and it correctly reported that the RAR files couldn't be extracted because they appeared corrupted (error 1166, due to RAR4 not being able to read RAR5 archives). Hence the v4 code does appear to be correct. I don't know off-hand what happened on orgatrain's system, but I'm not going to spend more time on it, since v4 (and above) appear fine to me, and v4 is fully de-suppoted anyway.