Glad that you were able to get a resolution. Only that uninstalling apps and the pain that goes with all that might get irritating if you run into this situation again and again. Was there anything in windows log to indicate the source of your problem?

Like I mentioned, when built with a earlier version of SSRS, the newer dev environment will attempt to upconvert that report. So before that even happens take a backup of the current .rdl file (especially if you are not using source control).