When you publish new version of InfoPath or update certificate for the form, some users may still see the old version or have issues with new certificate. Clearing InfoPath Cache in users machine resolves this issue.
When user access an InfoPath form, it is usually cached in users machine. Whenever there is a new version of form available, this cache should be cleared and updated with new version. In some cases, it should be cleared manually.
InfoPath Cache location in you machine:
Windows 7/8: C:\Users\[UserName]\AppData\Local\Microsoft\InfoPath\FormCache2\
Delete the folder named with GUID. This will clear all the cached forms. If you want to delete just that particular form, it’s upto to find the related files to that form and delete in that folder.
Clearing InfoPath cache from command line:
Start > Run> Infopath /cache clearall