I am having a repeated problem where I check out a document, but am not able to discard my checkout subsequently. What could be the cause? Background: I am a user not an administrator; our SharePoint Foundation 2010 system was set up some time back and we no longer have SharePoint experts onsite, so I suspect things have gotten outdated.
This might be because you have uploaded a document which has no checked in version, so Sharepoint cannot discard the check out as there would be no previous version.
Instead, try checking in the document - then checking it out again. After doing this, you might be able to use the Discard check out feature.