I have tried the above suggestions but it did not work for me.
I am installing my InfoPath forms via a feature.
What did work was doing a force install. e.g.
“C:\Program Files\Common Files\Microsoft Shared\web server
extensions\12\BIN\stsadm.exe” -o installfeature -filename
“Matrix.InfoPathFormV2.0\feature.xml” -force
Then doing ...