You should perform full on-demand scan under safe mode. Try to get sample which to upload to McAfee Labs and in the next 2-3 days they will create Xdat(extra detextion file) which could help you.
To find that virus you could use MS Autoruns.Also you could increase the Heusristic level that helps in many cases.
I think this might belong in the Business section, or perhaps in Security Awareness ....
Are you having this problem with McAfee's Enterprise (corporate) software, or with the Home & Home Office edition? What version of McAfee have you got installed?
Is it occurring on your server, or on clients on the network?
Could you take a screenshot of the messages? In the Home edition these display an exploit name, so perhaps yours will show more detail.