Note to self – Before developing on SharePoint, always enable debugging on the development machine to see a “little” more verbose error messages. Edit the web.config and change the following:
<SafeMode MaxControls="200" CallStack="false" ...> <!-- Becomes -->
<SafeMode MaxControls="200" CallStack="true" ...>
<customErrors mode="On" /> <!-- Becomes -->
<customErrors mode="Off" />
<compilation batch="false" debug="false"> <!-- Becomes -->
<compilation batch="true" debug="true">