**I already solved this question, this Q&A is purely for future Googlers since it was extremely difficult for me to find the solution via Google - but thanks for looking**

I changed my project to GWT 2.3.0 but then had to change back to 2.0.3 (in Eclipse) and now when I run it and try to view it in my browser, I get the following error:

> 
> [ERROR] Invalid version number "2.1" passed to external.gwtOnLoad(), expected "2.0"; your hosted mode bootstrap file may be out of date; if you are using -noserver try recompiling and redeploying your app
> 
> 
> 

I've tried cleaning and rebuilding and that doesn't work. How do I fix it?