Certain users get "Insufficient Security Privilege - This form cannot be opened because it requests domain security level and is only allowed restricted security level. Contact the form author to resolve the issue."
1. Clear the Internet Explorer Cache
2. Delete all files under %UserProfileFolder%\Application Data\Microsoft\InfoPath
Should actually be only 1 file, infopath.tbs.
3. Delete the cache in %UserProfileFolder%\Local Settings\Application Data\Microsoft\InfoPath\FormCache2 - For Office 2007 or FormCache1 for Office 2003
Problem should be sorted.