Got this error after migrating a SP2007 application to SP2010.

Activation could not be completed because the InfoPath Forms Services support feature is not present.

The feature it is complaining about is a hidden feature with displayname IPFSSiteFeatures. This feature was already enabled on the migrated application…but resolving the error was as simple as disabling and then re-enabling the feature. Here’s the PowerShell to do that:

Disable-SPFeature "IPFSSiteFeatures" -url "http://yourwebapp";
Enable-SPFeature "IPFSSiteFeatures" -url "http://yourwebapp";