"Unable to load document from identifier" error is mostly attributed to some dangler reference.
The Workflow/webApp might be referencing a temporary table which is now purged, or if it was copied from some other entity, the copied Activities might be having some previous reference which aren't valid now.
At times, this is also related to some process (essential for the Workflow/webApp to successfully execute) not running.
I believe you are working with a webApp, if so, then was this copied/imported from some other webApp.
Are there some more details which show up in Logs.
When you say a pop up box has been added for more details on the row selected, maybe some reference to this row of data is causing issues.