Onedrive (Skydrive) Sync issues through TMG

Question

We are having a ton of issues when using Onedrive (skydrive) to sync document libraries with our SharePoint 2013 server behind Forefront TMG. Users will randomly stop syncing (with no errors on skydrive), or files will just sit there trying to upload. I
checked the logs on forefront, and see the following error occurring quite often for the document libraries the users are trying to sync.
 12210 An Internet Server API (ISAPI) filter has finished
handling the request. Contact your system administrator.
We have an array of TMG servers that use FBA for authentication on the front end, then delegate using NTLM to the sharepoint server. The array is also setup as a reverse proxy, and is the only way the sharepoint server can reach the internet. We are using
the external host name (portal.domain.com) from TMG's internal adapter to the sharepoint server, so it's not a mapping issue. It's also happening on images and files that are less than 100KB, so it's not a size issue either.
I have tried disabling the malware filter completely, but the error still occurred. This is happening to multiple users running both windows 7/8.

Answer 1

I have no way to test this as our sharepoint server is in a remote datacenter, with no access except through TMG.
I did however get rid of the error by changing the authentication delegation method from NTLM to Basic. Since making the change, I have not seen any instances of the 12210 error for any users through TMG. So far I have no gotten any complaints/issues since
making the change.
So it looks like TMG cannot properly handle using NTLM to delegate the credentials. This is the second time I have run into an issue where this was the cause, and changing to Basic was the fix (Completely separate issue with TMG/IIS 8 using Ajax. Changing
to basic was the solution given by MS support)... It's pretty dumb that a Microsoft security product can't properly handle windows authentication on the back end....