When a WSP package is deployed it installs all features of the package to the desired web-application, but beside that it also installs them to the web-application that hosts the central administration (CA). This can cause problems, if the feature isn’t uninstalled correctly from all web-apps including CA. The problem is that it can leave behind features on the CA webapp, but not on the webapp the WSP was originally deployed to, when this is the case the WSP can’t be deployed again to the original webapp without using the force attribute like:
stsadm -o deploysolution -name $(SolutionName) -immediate -allowgacdeployment -url http://$(ComputerName):$(Port) -force
This is less than optimal.
When above is the case the features must be uninstalled manually from the webapps that still host them. But it can be a pain to find them, here Feature Wally comes in handy as it can search a webapp for installed features either by name or feature id.
http://featurewally.codeplex.com/
Update:
I just realized that theres an even better tool for this task, called featureadmin, this GUI tool simply eradicat all traces of a specific feature from everywhere in your farm. It can be downloaded from
http://featureadmin.codeplex.com/