We recently went to the Office 365 with our Lync communications. The Lync transition went smoothly, but a day into the change in our environment we noticed that SharePoint Designer 2010 workflows were giving us an error stating that “SharePoint Designer cannot display the item” and one of the causes could be a that it has been deleted from the site.
After the initial panic that the workflow may actually be gone and realizing that it was still intact, other were experiencing the same problem it became time to identify the problem. It seems this is a documented issue when organizations move to Office 365 for SharePoint. What was interesting is that our SharePoint is still on-premise. It is only our Lync communication that is now in Office 365 but it created the same result.
The trick was to get everything working again was to delete the SharePoint Designer Proxy Assembly Cache and then try opening the workflow again. This works with both SharePoint Designer 2010 and 2013. The Cache files are located at C:\Users\yourname\AppData\Roaming\Microsoft\SharePoint Designer\ProxyAssemblyCache
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