one of my users received an email attachment that is compressed with .zip format. She claims that she was able to open prior to her computer upgrade directly from the email. Is there a software that the user will need to install or any setting in outlook 2010.
Why don't you try clearing the Outlook secure temp folder. Check this link to know where this folder is located:
Outlook secure temp folder location (http://www.groovypost.com/howto/microsoft/outlook/find-the-microsoft-outlook-temporary-olk-folder/)