This error occurs when there are large files in history, causing a timeout communicating with the AppServer.
To resolve this, follow the steps below.
Run a CDH export to output all files from the case history (Tech four training required).
Sort the list of files by size.
Starting with the largest files - browse through the _docs\archive and temporarily exclude the file from the CaseViewer export by prefixing the filename with an X.
Repeat until the CaseViewer export is successful.
Once complete, remember to rename the files otherwise they will no longer be visible in history.
Note: If there are any .pdf files 2GB or more, exclude all of these first.
If any of the excluded files are required, you need to copy them and take them alongside the CaseViewer export.
If you're unable to follow the steps above, please raise a new case online and reference the title of this article.