Dave,
it seems you have an old implementation of (and/or local modification to) the bundle/commands. I would suggest moving all GTDAlt related items (including the GTDAlt.tmbundle folder) away from the ~/Library/Application Support/TextMate/... folders (both under "Pristine Copy" and under "Bundles") and onto your desktop or something. Then follow the instructions in: http://macromates.com/textmate/manual/bundles#installing_a_bundle for installing the version of the bundle that is in the repository. You will also need to check out: http://macromates.com/svn/Bundles/trunk/Support
the absence of this second updated repository is why you are getting the "lib/dialog" errors. See my correspondence on the list with Stefan Brantschen for details.
Haris