Though I could see most of the posts adhering to the topic are purely about wireless connections prompting for "Additional log on information may be required", this happen quite frequently with wired connections as well.
Windows 2008 AD Domain, ISA 2006 SP1 proxy, and 95% clients using Windows XP Pro 32bit with SP3. Ever since, we from IT has started lab testing Windows 7 Pro 64bit and 32bit clients, came across Additional log on information may be required or domain network showing "no internet access" false error messages.
We had gone through extensive ways to track and fix the problems.
1. Enabling the wpad.domain.com with DNS server solved most of the computers with these messages, while
2. Upgrading the NIC drivers
, disabling the sleep mode (power options) etc has resolved few others problems with network connections.
3. However, what we had assessed that, somehow, Windows 7 doesn't pass the user authentication tickets to ISA 2006 properly which was mostly the culprit.
Hope the information is useful for others who are suffering out there because of this MOST annoying part of Windows 7.