Thanks @Antipodes! Seeing it as a crash rather than an installer glitch was the ticket. I ran again without the Profiler attached and had no further trouble.
OK - glad to hear. The 1.6 build was crashing daily for me for the last months. Support seemed to think it was something about other software I was running - I am on Win 7 64. I had a crash after the download completed on the first go through and so had to restart 1.6 RM and download all over again which is thankfully very quick these days. On the second run through I got the installer pop-up and ran it to completion.
BTW - installing betas kills my RM shortcut on the desktop which points to nothing after the update. I have to launch from the start menu. Then when the thing goes full release I need another new RM shortcut to launch it.
GIven that you cannot run the full version and a beta update at the same time it might be better to maintain the shortcut somehow.
BTW - the new RM beta 2.0 seems more stable for me so far so that is good news. Looking forward to the editor.