Hi Markus and Eric,
we have the same problem as you – we developed an VSTO Add-In (but for Word 2013) and are running into trouble with the IsolatedStorage with the OpenXML SDK if the filesize gets bigger.
A couple of Months ago, we started to deploy our AddIn using the Windows Installer, instead of the ClickOnce-Deployment. At this moment we ran into issues with the IsolatedStorage (Exception-Message: “Unable to determine application identity of the caller”). After days of investigating and searching on google we found a working solution (see https://explodingmindslimited.wordpress.com/2012/08/31/openxml-and-powershell/). We had to create a new AppDomain for the OpenXml-things we are doing.
At the first look it worked well (and it still works fine for smaller documents), but for bigger files we still run into the IsolatedStorage problem. (Exception-Message: “Store must be open for this operation”)
Unfortunately we can´t remove the WindowsBase.dll aswell, because we need it for some WPF-Applications, the VSTO-Addin and the System.Windows.Threading.Dispatcher-Class.
Did you make any progress yet? It would be nice, if we can find out a solution for this.
Best regards,
Marcel