I was recently tasked with an issue where in the users of a sharepoint document library were unable to checkout documents.
The organization has a farm of 2 Web front end servers running Sharepoint 2010. The users when they are on the Intranet can check in and checkout documents absolutely fine. However when accessing this over the Internet, it fails the check in check out. The sharepoint application itself is published using the Microsoft Threat Management Gateway 2010. Since it works internally, the issue could be only on the TMG server 2010.
Internally the sharepoint runs on Port 80 (http) and externally over port 443 (https). This was the catch. verified the web publishing rule and found that the following was enabled in the sharepoint publishing rule.
– Forward the original host header instead of the actual one (specified in internal site name field)
disabled this and the users were able to check in and check out the documents over the Internet as well.
Hope this helps.