I was unable to find a reference to a similar problem anywhere online.
I've run XSI 6.0 on my computer forever, but when I tried to install the trial version of XSI 2010 and later 2011, I got the error message: "CMDREG.EXE has encountered a problem and needs to close" right before it completed. The program appears to be installed, but keeps asking for an Activiation key (even though its a trial version). Running the "runonce" command causes the same CMDREG message to appear. I have completely formatted my computer, running nothing but AVG antivirus and WIndows XP to make things simpler. Thankyou for any advice you can give!