Troubleshooting deployment errors in Sharepoint can sometimes be frustrating. Often you get some cryptic error and a inspiring message to "Please try again" when trying again really isn't going to make much of a difference.
How would you go about adding a custom built web part to a page in a site definition? MSDN shows an example using the <AllUsersWebPart> tag in the <module> section of a site definitions onet.xml file. Inside there is a CDATA area where it uses some more (presumably) XML to define and configure the web part. You can check out the example here: MSDN's AllWebUsersWebPart page. I had some issues adapting this to my own custom built web parts, which made me come up with the solution in this article instead.