Here's another post for you future googlers trying to track down the cause of an obscure InfoPath/SharePoint error message. In my own googlings, I found a number of questions about the problem, but no working solutions. I came up with the solution eventually... here it is.

The problem
...feel free to skip on down to the solution, past the irreverent narrative :-)

In today's episode, we look into the life and times of Hal the SharePoint server and Dave the Office user. Among his other assets, Hal hosts a Form Library, which holds XML forms submitted by InfoPath. Hal does all sorts of funky workflow on the forms behind the scenes, but that's another story.

Anyway, Dave has been happily InfoPathing for some time, beautifully oblivious to what's going on underneath the hood. But one fateful day, Dave can suddenly no longer submit his InfoPath forms to Hal. When he clicks the submit button, InfoPath barfs with:

InfoPath cannot submit the form.
An error occurred while the form was being submitted.
The form cannot be submitted to the following location: http://hal/sites/food/requests/Pie for Dave.xml
The site may be offline, read-only, or otherwise unavailable.

Alarmed, Dave's minions from the IT department come over and have a look-see. They notice that Dave can submit InfoPath forms just fine on the PC down the hall. It's definitely a problem with Dave's PC. (Hal takes this in stride — of course it's not a SharePoint problem. Further evidence that he's infallible.)

So the IT dudes google the error message, and lo! The hotfix mentioned in KB 907652 looks promising. Half an hour later, the unreleased hotfix has been successfully extracted from the depths of Microsoft PSS. Life is good... at least until Dave points out that the patch didn't solve his problem!

The solution

Turns out that KB 907652 was a false lead in Dave's case (and, I suspect, in a number of other folks' cases as well). The real fix is our good friend KB 287402.

Much of Microsoft Office 2003's SharePoint integration is accomplished using the WebDAV protocol. (Technically, WebDAV is an extension to HTTP. And Microsoft has their own name for it, web folders.) A prime example of this is InfoPath, which submits to Form Libraries using WebDAV.

So when something goes wrong with web folders, something often goes wrong with InfoPath, too. This connection isn't readily apparent, but there you have it.

You be dead, foo'!

I'll leave you with this random tidbit: KB 287402 has a laundry list of things to try. In Dave's case, we hit gold on the third step, which involves deleting HKEY_LOCAL_MACHINE\SOFTWARE\Classes\CLSID\{BDEADF00-C265-11D0-BCED-00A0C90AB50F}.

Er, did Mr. T have a hand in this? Go on, just tell me you're not amused by first 4 bytes of that GUID. I dare you, foo'!