Office document in SP2010 won't open - Explorer fails, SDP fails.

Problem: Can't open Office documents (Word, Excel or PowerPoint).  Additionally can't connect to SharePoint using SPD2010 or Publish forms using InfoPath 2010.  Another effect has been that Windows Explorer won't display document library's.

Initial Hypothesis:  A colleague of mine Grzegorz Skorupa in Poznan figured out the issue using Fiddler.  Our site was running over SSL so he had to decrypt the response's and requests using Fiddler.  Fiddler was also used to intercept the requests from the Office client program.  From this he could see MS Word issuing more than simply GET and POST verbs.  Recently our SharePoint test environment had been hardened which include only allowing GET & POST verbs.  This also only occurs if you are using STSsession cookies.  This was previously discussed http://blog.sharepointsite.co.uk/2010/11/change-to-session-cookies-for-claims.html

You can check your farms cookies session setting using the following PowerShell cmd:
PS> Get-SPSecurityTokenServiceConfig

As it has been explained to me, because the session cookies are being used, the cookies are no longer written to disk, so the Office application needs to authenticate (as it can't use the cookie created by the SharePoint browser session). The Office client uses WebDAV request, has to authenticate and it passes requests that are not GET or POST based to retrieve the file.

Resolution:  Check IIS and the instances of IIS are allowing all verbs in request filtering or use the default sessioncookies setting (false).

$sts = Get-SPSecurityTokenServiceConfig
$sts.UseSessionCookies = $false
$sts.Update()
iisreset

You can watch the http request types (request verbs) using Fiddler as highlighted below.