The Right Stuff of Tahoe

Same "NSIS error launching installer" problem (for version 5.63.7540). Happened on two venerable XP SP3 machines (which we still use for regression tests of software we write). Arrived at a hack-fest solution, based on longstanding fact that CCleaner install overwrites existing installed version (even unfortunate versions, released after AVAST began butchering it). If your luck is as good as ours, this works even if you install an older version. Reinstalled 5.55.7108 on top of 5.63.7540 (we keep at least one Ccleaner version going back). Then could use Add or Remove Programs (one of the offending XP machines) or, indeed, CCleaner 5.55.7108 (the other offending XP machine) to uninstall resp. remove CCleaner 5.55.7108. Upon reboot, doublecheck for orphaned copies of CCleaner.exe and CCUpdate.exe in your master volume (typically, drive C:). I deleted 'em both, on both XP machines. Too bad that AVAST has spoiled what used to be a nice utility. As far as my shop is concerned, CCleaner is consigned to the dustbin. Q.v. this recommendation agsainst any version post 5.45 https://betanews.com/2018/08/01/do-not-install-the-latest-version-of-ccleaner/