If you have ever run into the issue where you can’t publish an InfoPath form to a specific site because the ‘Enable this form to be filled out by using a browser’ option is disabled in the publishing wizard, here are a couple suggestions.
Example of option being disabled in the InfoPath publishing wizard:
Enterprise Features
Check to make sure that the “Office SharePoint Server Enterprise Site features” are enabled on the site that you are trying to publish the form to.
If it is already enabled, you will likely need to try the next option.
Re-enable the InfoPath Form Services feature on the site collection and site
Replace <SiteURI> with the sub-site URI
Replace <SiteCollectionURI> with the site collection URI
Run this on the central admin SharePoint server:
stsadm -o deactivatefeature -filename IPFSWebFeatures\feature.xml -force -url <SiteURI>
stsadm -o deactivatefeature -filename IPFSSiteFeatures\feature.xml -force -url <SiteCollectionURI>
stsadm -o activatefeature -filename IPFSSiteFeatures\feature.xml -force -url <SiteCollectionURI>
stsadm -o activatefeature -filename IPFSWebFeatures\feature.xml -force -url <SiteURI>
Note: if you are working with a site that is the root site in a site collection, <SiteCollectionURI> and <SiteURI> will be the same.
Dan Myhre's Blog 