I am sure this error...
Unable to locate specified base class 'com.esri.solutions.flexviewer.BaseWidget'
...is caused by my attempt to upgrade to flex viewer 2 and flash builder 4. Is the BaseWidget information located in a different area or is there a major overhaul required in order to fix this problem.
This error occurred when I placed the IdentifyWidget from the old code forums into my new flex app.
Thanks!