Hey Brian,
I also experienced exactly what you describe, on the f5419a. It was solved by installing the latest patch of the IAR (5.6.6). They also list it as a bug fix in the release notes. The FET must be updated accordingly (this also doesn't work smoothly, I also stopped using the latest version of FET-pro-lite, since they do not agree on the latest version of the FET driver).
thanks :)