There was some disturbing news for Microsoft this week: A study found that less than 25% of corporate PCs running XP have upgraded to SP2. This, even though SP2 is a significant security upgrade, and offers a better wireless client than pre-SP2 XP.

The study didn’t question why the adoption rate is so low, but it’s most likely because of compatibility issues with custom-built applications. The Windows Firewall is turned on by default in SP2, and it has caused numerous problems with custom apps, as well as some off-the-shelf ones.

That news is bad enough. Worse, though, is that Microsoft can likely expect a much-lower adoption rate for Longhorn, when it’s released, possibly some time next year. After all, from XP to XP2 is an upgrade of the same operating system. From XP to Longhorn is an upgrade to an entirely new operating system, with different plumbing underneath. Expect compatibility issues to be severe, and so companies may well stay away in droves.

This will have a much more serious impact on Microsoft than the upgrade to SP2. Microsoft received no revenue from the upgrade to SP2. It’s likely hoping for a massive revenue boost from Longhorn. If the SP2 upgrade is any indication, it won’t get it.

Could this mean Longhorn will be dead on arrival? For consumers, the answer is no — when you buy a new PC off the shelf, you won’t have a choice of operating systems, and so you’ll get Longhorn. But for enterprises, the answer may well be that Longhorn is DOA. And that means potentially big financial problems for Microsoft.

Do you think Longhorn may be DOA? Let me know.