Try running a find utility to grep through the source code, to see if there's a hidden reference -- for example, some dormant reference that can easily be removed...
(If you're running cygwin or UNIX tools suite for win32, you use this below command)
c:\cygwin\bin\find c:\projects\BBWeather -exec grep -i "StringBuilder" {} ;
or if your command line grep.exe supports recursion,
grep -r -i "StringBuilder" c:\projects\BBWeather
Or instead, use the 'search' feature of your development environment. (as long as it follows folders recursively, and can search all files including non-source-code files, even binary files...)
Any of the above may reveal a file that pinpoints hidden references to an obsolete class. Hiding deep inside an old makefile, a definition file, a configuration file, a project workspace file, even if the reference is not in the source code itself... Even an old object file that's inadvertently recycled (this can happen with some development environments, if installing a project inadvertently includes object files that the compiler doesn't overwrite, if it thinks it's current)
P.S. Please note, I am not the developer of BBWeather, so can't answer specific questions about BBWeather. However, I'd like one of you BBWeather developer to add an automatic "area code" search into BBWeather, so I can just type in the city name instead of trying to remember 8-character codes such as CAXX0351. It may be as simple as sending a regular HTML search query
http://www.weather.com/search/enhanced?where=<cityname> to
weather.com and then parsing the resulting HTML screen for the 8-digit code. There may be multiple search results, so if that happens, just pop up a BlackBerry screen giving a choice of matching search results.