Weirdest error ever.
I use the feature upgrade toolkit from Chris OBrien on a daily basis and today I got this exception when upgrading a feature. And I have not feature with the name #comment. Lol
The thing is apparently you can not put xml comments on template.xml fields!!
<!–<CustomUpgradeAction Name=”MyMethod” />–>
This wont work, just remove it from the template.xml file.