My custom module is generating this error on the system log everytime I try to view the indexController.
2012-01-25T17:23:08+00:00 CRIT (2): Not valid template file:adminhtml/base/default/template/page/2columns-right.phtml
I've been fishing through my module code for hours, just can't seem to find anything wrong. What could cause this? The base/default folder doesn't even exist under adminhtml.
The "base/default" package/theme is the final folder Magento will look for template files in. When you see this error, it means Magento looked for the template in
[current-design-package]/current-theme/template/page/2columns-right.phtml
[current-design-package]/default/template/page/2columns-right.phtml
There's not enough information in your question to 'suss out the exact problem you're having, but it looks like you have, by your self or via a third-party-module, made an attempt to change the template of the root block (or perhaps another block) in the Magento admin console application to 2columns-right.phtml.
However, this template does not exists anywhere in the adminhtml design package. That's why you're getting that error. There's only one root template that ships with the admin console, and that's page.phtml. The 2columns-right.phtml template is a frontend template, for the cart application.
If that doesn't help a better description of your module, as well as your motivation for using it and what you expect to happen will be needed for anyone to answer your question.