Confirm this is an AV problem. McAfee "real time scanning" was the culprit for me. Turning it off allowed PAINT.NET to install.
I did get a couple of pop-ups saying: "COM Surrogate has stopped working." I don't know if that's related to the install, however.
This thread should be summarized with the initial post and included in Rick's install / troubleshooting thread, perhaps with the post about "Disable A/V software". I don't think that generic admonition is sufficient. The error message above is a pretty definitive problem signature - if I had seen it at the outset, it would have saved me 20 min of fumbling around the site (I finally searched for the string "IterativeTask" to get here.)
