Question : SharePoint 2010 Upgrade Error: The missing feature may cause upgrade to fail. Please install any solution which contains the feature and restart upgrade if necessary.

I'm getting the following error in my preupgrade check and during my test upgrade:

The feature with Id ___ is referenced in the database ___, but is not installed on the current farm. The missing feature may cause upgrade to fail. Please install any solution which contains the feature and restart upgrade if necessary.

We migrated from 32 bit servers to 64 bit servers recently and there are probably solutions that we installed long ago on the old servers.  We don't have the files to reinstall the solutions on the new servers...and actually don't care to reinstall since they are not in use.  Is there a way to clean out these references?

Answer : SharePoint 2010 Upgrade Error: The missing feature may cause upgrade to fail. Please install any solution which contains the feature and restart upgrade if necessary.

I had issues on the preupgradecheck report which carried forward into the test upgrade.

I put some notes into how to fix the items on the preupgradecheck here: http://www.experts-exchange.com/OS/Microsoft_Operating_Systems/Server/MS-SharePoint/Q_26264249.html

Not out of the woods yet since I still am running into a "A duplicate content type name "Resource" was found." error even though the preupgradecheck report was clean.  I'm going to close this question and leave the other open as cleaning up the preupgradecheck report is better than trying to clean up after a failed upgrade.